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The growing scarcity of potable water supplies is among the most important issues facing many cities, in particular those using single sources of water that are climate dependent. Consequently, urban centers are looking to alternative sources of water supply that can supplement variable rainfall and meet the demands of population growth. A diversified portfolio of water sources is required to ensure public health, as well as social, economical and environmental sustainability. One of the options considered is the augmentation of drinking water supplies with advanced treated recycled water. This paper aims to provide a state of the art review of water recycling for drinking purposes with emphasis on membrane treatment processes. An overview of significant indirect potable reuse projects is presented followed by a description of the epidemiological and toxicological studies evaluating any potential human health impacts. Finally, a summary of key operational measures to protect human health and the areas that require further research are discussed.
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Int. J. Environ. Res. Public Health 2009, 6, 1174-1209; doi:10.3390/ijerph6031174
International Journal of
Environmental Research and
Public Health
ISSN 1660-4601
Indirect Potable Reuse: A Sustainable Water Supply Alternative
Clemencia Rodriguez 1,*, Paul Van Buynder 2, Richard Lugg 2, Palenque Blair 3, Brian Devine 1,
Angus Cook 1 and Philip Weinstein 1
1 School of Population Health, Faculty of Medicine, Dentistry and Health Sciences, The University
of Western Australia, 35 Stirling Hwy, (M431) Crawley WA 6009 Western Australia, Australia;
E-Mails: (B.D.); (A.C.); (P.W.)
2 Department of Health, Government of Western Australia, Grace Vaughan House 227 Stubbs
Terrace, Shenton Park, WA 6008 Western Australia, Australia;
E-Mails: (P.B.); (R.L.)
3 Water Corporation, Western Australia, 629 Newcastle Street, Leederville, Perth WA 6007 Western
Australia, Australia; E-Mail:
* Author to whom correspondence should be addressed; E-Mail:;
Tel.: +61-(08)-6488-1224; Fax: +61-(08)-6488-1188
Received: 22 December 2008 / Accepted: 11 March 2009 / Published: 17 March 2009
Abstract: The growing scarcity of potable water supplies is among the most important
issues facing many cities, in particular those using single sources of water that are climate
dependent. Consequently, urban centers are looking to alternative sources of water supply
that can supplement variable rainfall and meet the demands of population growth. A
diversified portfolio of water sources is required to ensure public health, as well as social,
economical and environmental sustainability. One of the options considered is the
augmentation of drinking water supplies with advanced treated recycled water. This paper
aims to provide a state of the art review of water recycling for drinking purposes with
emphasis on membrane treatment processes. An overview of significant indirect potable
reuse projects is presented followed by a description of the epidemiological and
toxicological studies evaluating any potential human health impacts. Finally, a summary of
key operational measures to protect human health and the areas that require further
research are discussed.
Int. J. Environ. Res. Public Health 2009, 6
Keywords: Chemicals of concern; health impacts; risk assessment; recycled water.
1. Introduction
With climate change, population growth and water scarcity, there is a growing need to manage
water resources in a sustainable manner. Worldwide, 1.1 billion people lack access to adequate water
supplies [1] and there is an increased pressure on the world’s freshwater sources. Many large rivers,
particularly in semiarid regions, have significantly reduced flows and the abstraction of groundwater is
unsustainable, resulting in declining water tables in numerous regions [2-4]. Therefore, the use of
recycled water has become an increasingly important source of water. Water-recycling projects for
non-potable end uses are a common practice with more than 3,300 projects registered worldwide in
2005 [5].
Indirect potable reuse (IPR) is one of the water recycling applications that has developed, largely as
a result of advances in treatment technology that enables the production of high quality recycled water
at increasingly reasonable costs and reduced energy inputs. In IPR, municipal wastewater is highly
treated and discharged directly into groundwater or surface water sources with the intent of
augmenting drinking water supplies [6]. In this review paper, recycled water refers to wastewater from
sewage treatment plants treated to a level suitable for IPR. Unplanned or incidental use of wastewater
for drinking purposes has taken place for a long time. This occurs where wastewater is discharged
from a wastewater treatment plant to a river and subsequently used as drinking water source for a
downstream community. In contrast, this review focuses on planned IPR. The use of environmental
buffers such as rivers, dams, lakes or aquifers is considered world’s best practice given that natural
systems have a high capacity to further purify water [7]. Retention time of the recycled water in the
raw water supply allows any remaining contaminants to be degraded by physical processes (e.g.
natural ultraviolet light) or biological processes (e.g. ‘native’ micro-organisms). Storage of the
recycled water for a period of time before consumption provides an interval of time in which to either
stop delivery of water or to apply corrective actions in the event of a treatment failure. Dilution of
recycled water in the environmental buffer also minimizes any potential risk by decreasing the
concentration of contaminants that may be present.
Cities with limited water resources are considering IPR as a feasible option for the sustainable
management of water because it is a water supply alternative not dependent on rainfall and it is
possible to achieve high quality recycled water in compliance with drinking water standards and
guidelines. IPR has the potential to make a significant contribution to urban water resources needs but
a cautious approach is required to manage the health risk associated with recycled water for drinking.
The number and concentration of chemical and biological hazards in wastewater is far higher than the
potential hazards that could be found in pristine waters. Contaminants have been detected at low
concentrations in highly treated recycled water and any potential health impacts need to be evaluated.
Moreover, there are currently no health values for most of these contaminants and usually there are
limited toxicological information available. Therefore, an analysis of potential human and
environmental risks and the involvement of the community before any implementation proceeds need
to be carefully undertaken on a case-by-case basis. This paper presents the “state of the art” context of
Int. J. Environ. Res. Public Health 2009, 6
water treatment, the lessons learned from existing projects and the issues that require further research
from the public health perspective. Three supporting tables are provided; Demonstration and full-scale
IPR projects (Table 1), Epidemiological studies (Table 2), and Toxicological studies (Table 3).
2. Existing Indirect Potable Reuse Projects
IPR is not new and has been successfully implemented in the United States (US), Europe and
Singapore. In the US, California is the leading state with the highest number of IPR projects and more
than 40 years experience; other states with demonstration or full-scale IPR projects include Arizona,
Colorado, Texas, Florida and Virginia. In California, Water Factory 21, in the Orange County Water
District (OCWD), is the oldest project, with a production capacity of 19 megalitres per day (ML/day).
Water Factory 21 was closed in 2004 and the upgraded groundwater replenishment system (GRS)
plant was completed in 2007. The GRS produces 265 ML/day with an ultimate capacity of 492
ML/day [8].
Table 1 provides a summary of 14 well-documented IPR projects around the word. The majority of
the projects operate in the US, half of these projects were implemented before the 1980s and four were
demonstration plants. The Tampa, San Diego and Potomac demonstration projects aimed to evaluate
the feasibility of augmenting drinking water supplies with recycled water, whereas the Denver
demonstration project aimed to study the viability of direct potable reuse. The environmental buffers
used are mainly aquifers and reservoirs before drinking water treatment. The population served varies
from 60,000 inhabitants in the Torreele’s water reuse facility in Belgium to more than 2.3 million in
the GRS (OCWD) project.
Other projects in the US have also implemented IPR (not included in Table 1), such as the Gwinnett
County Department of Public Utilities, Lawrenceville, Georgia; Inland Empire Utilities Agency,
Chino, California; Water Campus, City of Scottsdale, Arizona; El Segundo, California; Tahoe-Truckee
Sanitation Agency Water Reclamation Plant, Reno, Nevada; Loe J. Vander Lans Advanced Water
Treatment Facility, Long Beach, California; and Northwest Water Resource Centre, Las Vegas,
Nevada [9]. All these projects have been supported by their communities and they follow the
respective federal or state regulations related to recycled water.
Numerous cities in Europe rely on unplanned IPR for approximately 70% of their potable water
source during dry conditions [10]. The IPR project in Wulpen, Belgium, discharges recycled water to
an unconfined dune aquifer. Initially the recycled water comprised 90% reverse osmosis (RO)
permeate and 10% microfiltration (MF) permeate. However, it was observed that some herbicides
were present in the recycled water at levels below drinking water standards due to detection of
herbicides in the MF permeate. As a result, since May 2004, only the RO permeate is injected into the
aquifer with addition of sodium hydroxide to adjust the pH [11].
In Singapore, a demonstration facility at Bedock Water Reclamation Plant was commissioned in
2000 to evaluate the performance of a dual membrane technology to reliable produce recycled water
for IPR and high grade quality water for industry use [12]. Three additional water reclamation plants
were commissioned at Kranji (2002) and Seletar (2004) and Ulu Pandan (2007) producing
approximately 200 ML/day [13].
Int. J. Environ. Res. Public Health 2009, 6
In Australia, there are some projects considering the use of IPR through aquifer recharge or dam
supplementation, but none as yet implementing potable reuse. IPR has been proposed for Toowoomba
(Queensland), Perth (Western Australia), Goulburn (New South Wales) and South East Queensland
[14]. In the City of Perth a pilot IPR trial will inject up to 5 ML/day of MF/RO and ultra violet (UV)
light disinfected recycled water from the Beenyup Wastewater Treatment Plant (WWTP) into the
Leederville aquifer (a major drinking water source for the metropolitan area). If this pilot trial
successfully demonstrates no health or environmental impacts, a full-scale project is proposed by 2015
[15]. The City of Goulburn, New South Wales, is also seeking support for a project to supply its dam
with recycled water. Goulburn is undertaking lengthy community consultation on all its available
water management options, but in 2008 41% of local people surveyed considered IPR undesirable
The Toowoomba project, which aimed to add recycled water to supplement the drinking water
supply of the Cooby Dam, did not receive community support in a referendum held in July 2006, with
62% of votes against IPR [17]. Nevertheless, the Queensland Government supported the Western
Corridor Recycled Water Project, which included Toowoomba, with a capacity to produce 182
ML/day of recycled water for industrial and potable purposes including supplementation of Wivenhoe
Dam [18]. Given the critical water supply situation in Queensland, the community was more
sympathetic to the project in late 2007 and early 2008, but due to increased rainfall in the region that
increased the dam capacity above 45% they were less supportive in late 2008. As a consequence,
despite having built three advanced treatment plants for recycled water, at the end of 2008, the
Government changed its recycled water policy from continuous use of IPR to emergency use when
dams fall below 40% capacity.
3. Studies on Health Effects
Despite variations in treatment technologies, environmental buffers used, proportions of recycled
water blended with the raw drinking water sources (from 1% to 100%), and estimated retention times
in the receiving waters (from 40 days to several years), none of the projects listed in Table 1 have
reported adverse health impacts in the communities served.
In 1998 the US National Research Council (NRC) published the evaluation and recommendations
of a multidisciplinary team of experts that explored the viability of augmenting potable water supplies
with recycled water. The report concluded that, from the information available, the risk from IPR
projects were similar to or less than the risks from conventional sources, but nonetheless considered
that IPR should be an option of last resort [7].
3.1. Epidemiological Studies
There are few published epidemiological studies on potable reuse and a summary is presented in
Table 2. In Windhoek, Namibia, potable reuse was implemented in 1968 and it was initially used
sporadically when drought conditions made it necessary. An ecological study conducted in Windhoek
examining diarrhoea and type of water supplied concludes that differences in diarrhoeal disease
prevalence was associated with socio-economic factors, but not the nature of the water supply [7]. So
Int. J. Environ. Res. Public Health 2009, 6
far, no studies have been conducted in the Windhoek project examining long-term potential health
impacts of micropollutants in drinking water.
In the Montebello Forebay project, three epidemiological studies were published, two of them using
an ecological design. The latest ecological study was published in 1996 (Table 2). In this study, a
significantly higher incidence rate of liver cancer in the area with the highest percentage of recycled
water was observed. However, no significant trend was observed when comparing liver cancer incidence
over different exposure categories, and the authors concluded that the positive association occurred by
chance. The study does not provide evidence that recycled water has an adverse effect on cancer
incidence, mortality or infectious disease outcomes. However, the ecological studies performed thus
far have been limited by their design and the corresponding difficulties that arise in the accurate
assessment of the exposure [19]. A cohort study examining the association between the use of recycled
water and adverse birth outcomes, including 19 categories of birth defects, was conducted from 1982
to 1993. This study did not find any significant association between the use of recycled water and
adverse birth outcomes, and rates were also similar in groups receiving high and low proportions of
recycled water [20].
No prospective studies have been conducted examining the potential adverse health effects of long-
term exposure to low concentration of chemical contaminants from potable reuse. However,
assessment of exposure is especially challenging in studies with long latency periods, such as cancer.
In the late 1990s the OCWD and an independent scientific advisory panel suggested conducting a
case-control study on the use of Santa Ana River water. However, the study was found to be non-
feasible due to limitations in assessing historical exposures. The panel did not recommend any
additional epidemiological studies because any incremental risk due to recycled water is likely to be
extremely small and difficult to differentiate from normal background risk [21]. The panel instead
recommended a focus on monitoring to verify the effectiveness of the treatment processes.
Given that epidemiological studies of long latency (such as cancer outcomes) are associated with
many competitive risk factors and are complicated by limitations in the assessment of the exposure,
epidemiological studies with health endpoints of short latency (such as gastrointestinal diseases or
adverse pregnancy outcomes) may be more appropriate as a means of elucidating possible disease
pathways. A critical aspect for projects considering the implementation of epidemiological studies is
the need to carefully assess the exposure to recycled water in the study population during the period of
interest. Hydrogeological modeling, geographic information systems and exposure data at the
individual level may be required to link health outcomes with levels of exposure to recycled water.
3.2. Toxicological Studies
Toxicological testing is the primary component of chemical risk assessments of IPR projects.
Estimations of human health risks from exposure to specific chemicals are generally based on
extrapolations of toxicological analyses on animals. Given that toxicological information exists only
for a small percentage of chemicals and that toxicological data for individual compounds are not
adequate for predicting risks posed by chemical mixtures, it is usually the concentrates of recycled
water which have been used to assess potential health risks [13]. Overall, toxicological studies have
Int. J. Environ. Res. Public Health 2009, 6
varied in approach and study aims, but no significant health risks have been identified from these
studies (Table 3).
In the US, only the Denver and Tampa studies assessed a wide range of toxicological endpoints.
These studies included sub-chronic and chronic toxicity testing, as well as specific health effects (such
as reproductive, developmental and carcinogenic outcomes). In these two demonstration projects and
in Singapore, toxicological analyses have been performed by comparing the health effects on animals
(usually rats and mice) fed over several generations with recycled water concentrates, compared with
control groups. The Denver report concludes “no adverse health effects were detected from lifetime
exposure to different concentrate samples during a two-generation reproductive sample” [22]. In
Singapore, the health effects testing programme also concluded that exposure to, or consumption of,
recycled water does not have carcinogenic or estrogenic effects on fish or mice [23]. Finally, the
Tampa study did not report any increased adverse health effects on animals fed with recycled water.
Mutagenic studies using the Ames test, which is used to determine whether a chemical is able to
cause cell mutations to the bacteria Salmonella typhimurium, were performed in the San Diego,
Tampa, Potomac Estuary, OCWD and Montebello Forebay projects. In general, less mutagenic activity
was observed in recycled waters compared to other water sources. In the Montebello Forebay project,
mutagenic activity was detected in 43 of the 56 samples from both recycled and control waters tested.
The observed level of mutagenic activity was maximal for storm runoff, but lower (in declining order)
for dry weather runoff, recycled water, ground water and imported water [24]. The Ames test is a
commonly used screening tool and is easy to perform, but may produce a relatively high proportion of
false positives and false negatives. Most of the mutagenic activity that was found appeared to be linked
to the chlorination process. However, identification of specific mutagens was not possible due very
low concentrations of contaminants but the National Research Council recommended further studies to
characterize the chemicals involved in the mutagenic activity of the recycled water given the
consistency of findings among the evaluated studies [7].
Bioassays conducted for estrogen, androgen, and thyroid activity have shown a progressive
endocrine activity reduction during the treatment train and a very low endocrine activity in the product
water [25]. Lee et al. reported low estrogenic activities (measured as estradiol equivalent
concentrations, or EEQ) of 0.23 and 0.05 ng-EEQ/L after MF and RO respectively. The estrogenic
activities were at markedly reduced values compared with the value of 1.2 ng-EEQ/L in the plant
influent. The bioassay EEQ measurement and the EEQ calculated from chemical analysis of known
estrogenic chemicals were similar for samples taken both after MF and after RO. However, the EEQ in
the influent was twice as high when calculated by chemical analysis compared with the bioassay, due
in part to antagonistic effects between chemicals. Consequently, the removals of endocrine disrupting
compounds in terms of the EEQ value from the biological and chemical determinations were 80 and
96% for MF and RO respectively [26].
4. Measures for Public Health Protection
A variety of factors must be carefully assessed to ensure public health protection. Some of the
fundamental practices and lessons learned from the implementation of IPR projects are presented in
this section. These factors include the treatment processes required to achieve high water quality; the
Int. J. Environ. Res. Public Health 2009, 6
quality of the existing water supply and any changes in this source after recycled water is blended;
system reliability; the regulatory framework and risk management practices.
4.1. Recycled Water Quality and Monitoring
Analytical monitoring programs of existing IPR projects listed in Table 1 have demonstrated the
effectiveness of advanced treatment in meeting all primary and secondary drinking water standards.
For example, in the NeWater project in Singapore, more than 190 drinking water parameters are
monitored, and the project consistently meets the requirements stipulated in the USEPA and WHO
drinking water guidelines [23]. Furthermore, all projects described in Table 1 have reported that the
treatment can reliably produce water of equal or better quality than that of the existing untreated or
treated drinking water supplies [21-23,27-29]. It is accepted that advanced treatment can produce
recycled water in compliance with drinking water standards and guidelines. Although this compliance
is fundamental to the protection of public health, it does not necessarily guarantee the safety of the
recycled water. Wastewater often comprises a complex mixture of domestic, industrial and agricultural
contaminants. Therefore, monitoring for contaminants either known or suspected to be present in
wastewaters at concentrations of concern needs to be implemented to demonstrate that the
concentrations of these contaminants, if present after the treatment, do not pose any additional health
Characterization of biological and chemical agents in the product water has been carried out in all
projects described in Table 1. Despite variations in treatment technologies and technological changes
over time, all IPR projects have demonstrated high removal efficiency for contaminants tested.
Removal of unregulated chemical contaminants was tested in the San Diego and Denver demonstration
plants [22]. In Denver, an organic challenge study tested the treatment efficiency in removing
chemicals. Fifteen organic compounds were dosed at 100 times the normal levels found in the
treatment plant influent, and the results demonstrated that the multiple-barrier process could remove
those contaminants to non-detectable levels [22]. In San Diego, the monitoring program demonstrated
the effectiveness of RO in removing metals, other inorganic compounds, and 29 pharmaceuticals and
personal care products, including caffeine and ibuprofen, typically found in wastewater from
secondary treatment plants [30]. Testing for non-regulated contaminants such as endocrine disrupters,
pharmaceuticals and personal care products is currently underway in many projects as part of
regulatory requirements or research interest. For example, in the GRS (OCWD) project, concentrations
of estrone, 17-α-ethynyl estradiol and 17-β-estradiol were all below the detection limit of 10 ng/L, and
caffeine concentration was below 0.1 µg/L in the recycled water [8].
Various guidelines suggest that the minimum log reductions required for IPR are: 8 log for
Cryptosporidium, 9.5 -10 log for enteric viruses and 8 log for Campylobacter [61]. MF is able to remove
protozoan oocysts and cysts, algae and some bacteria and viruses [31]. Viruses are the biological
contaminants of major concern in IPR, due to the large numbers present in wastewater and their small
size (range from 0.01 to 0.1 microns). Because pathogenic viruses have the potential to cause disease
outbreaks from a single spike of exposure, they are a high public health priority. MS2 bacteriophage
has been used to validate membrane performance. MF alone produced a 1.9 log removal of MS2
bacteriophage [32] and ultrafiltration and RO can provide 2 to 6 log removal [33,34] MS2 has been
Int. J. Environ. Res. Public Health 2009, 6
detected in RO permeate as a result of faults or damage in membrane structure [35]. In addition,
variable log removal has been reported with variable influent concentrations of MS2 [35] and the MS2
sensitivity to (UV) light was not constant [32]. These issues are complicated by difficulties in isolating
and measuring viruses and the cost of the analysis. The removal of virus by MF/RO is dependent upon
the particular membrane being employed and therefore the estimation of the removal or inactivation
credit for viruses ideally should be done on a “membrane by membrane” basis. Therefore, projects
considering IPR need to: identify membrane manufacturer studies to remove pathogens with special
relevance to virus, validate the treatment process using accredited methods and protocols; perform
suitable challenge tests for viruses to ensure the treatment efficiently removes these contaminants and
verify the integrity of the membrane systems through routine testing. Direct methods of membrane
testing, such as the pressure hold test and the diffusive air flow test, are very sensitive to identify
impaired membrane integrity but they cannot be applied while the plant is in operation. Indirect
methods such as particle counting, turbidity and conductivity are less sensitive but are continuous and
online, and can be used as surrogates to monitor membrane integrity. Therefore a combination of both
direct and indirect methods is recommended for a comprehensive monitoring program [34].
Chemicals that have been detected in secondary effluents include household and industrial
chemicals such as detergents, flame retardants, plasticizers, personal care products and
pharmaceuticals. Some of these compounds are known or suspected carcinogens, others are estrogenic
and have the potential to adversely affect the endocrine system. Advanced treatment technologies such
as MF/RO followed by advanced oxidation processes and/or UV are able to remove most of these
contaminants to levels below limits of detection (ng/L) [36-38]. It is important to note that organic
contaminants have also been detected in many other drinking water sources at low concentrations
(< 0.1 µg/L). The US GS Water Quality Assessment Program has determined that streams and rivers
used for public drinking water have low levels of about 130 chemical contaminants, most of them
without drinking water standards. Nearly two-third of these contaminants were also found in drinking
water. These results indicate that conventional drinking water treatment was unable to remove the
trace contaminants, and that unplanned potable reuse (as currently happens in many places in the
world) has the potential to result in large concentrations of micropollutants in drinking water supplies.
The most commonly detected chemicals were herbicides, disinfection by-products, and fragrances. A
median of 4 to 6 compounds were detected per site indicating that the targeted chemicals generally
occur in mixtures and that they originate from a variety of household and industrial sources [39,40].
Many IPR recycled water projects implement monitoring programs to evaluate the treatment
efficiency in rejecting organic contaminants, including endocrine disrupters, pharmaceuticals and
personal care products and other unregulated compounds. Antibiotics are of special interest because of
growing concerns over antimicrobial resistance in human medicine. Disinfection by-products may be
generated during the treatment process and some of them can be stable, polar and toxic, such as N-
nitrosamines and trihalomethanes. Their formation should be avoided or their removal accomplished
as far as possible in any potable reuse project. Endocrine disrupters (particularly those with an
estrogenic effect) produce adverse effects in fish and other species at low concentrations. Within the
framework of the precautionary principle, the reliability of advanced treatment in removing such
compounds to the maximum extent achievable needs to be demonstrated for the protection of human
Int. J. Environ. Res. Public Health 2009, 6
Drewes et al. recommended the use of chemical indicators and surrogates to monitor treatment
performance. They selected a list of wastewater-derived contaminants to determine the treatment
removal efficiency of individual unit processes commonly used in IPR (i.e., soil aquifer treatment,
ozone, advanced oxidation, chlorination, carbon adsorption, and RO). The authors validated the
removal efficiency of the selected chemicals for each unit process through laboratory, pilot, and full-
scale experiments. Different groups of chemicals, sharing similar physicochemical characteristics,
were detected at low concentrations (ng/L) for each one of the unit processes. The report concludes
that, by selecting multiple chemical indicators with different physicochemical properties, it is possible
to account for compounds currently not identified and new compounds synthesized and entering the
environment in the future, provided they fall within the range of properties covered. The underlying
concept is that absence or removal of an indicator compound during a treatment process would also
assure the absence or removal of other compounds with similar properties. For example, the authors
recommended the use of sulfamethoxazole, N-nitrosodimethylamine (NDMA), tris(2-chloroethyl)-
phosphate (TCEP) and chloroform as chemical indicators during the initial phase of the IPR project
and the use of conductivity, total organic carbon (TOC), and boron as surrogate parameters for the
MF/RO system [38].
4.2. Membrane Treatment and the Multiple Barrier Approach in Treatment
Ultrafiltration or MF as pre-treatment for RO followed by UV treatment or advanced oxidation are
the commonly used treatment steps in IPR. Secondary effluent from conventional wastewater
treatment plants is treated by MF, which is a low-pressure membrane with a pore size of 0.01 µm. MF
can remove most of the fine suspended solids (more than 99% rejection), colloidal solids, bacteria and
protozoa. [29,41-43]. After MF the water passes through the RO, a high-pressure process that forces
water through the porosity matrix of a specialized membrane. RO can reject high molecular weight
organic matter (characterized as humic and fulvic acids) [44] and total organic carbon rejection is
normally higher than 96% [28]. Removal of biochemical oxygen demand and chemical oxygen
demand has been reported as high as 98% and 96% respectively [28]. RO separates out minerals and
other contaminants, including heavy metals, viruses, and pesticides [43,45].
In the studies conducted so far, high percentages of organic contaminant removal are commonly
reported. RO can remove up to 95 to 99% of hormones [36,46], and more than 95% of all tested
analytes, including 16 pharmaceuticals and three personal care products [47]. In general, membranes
are able to reject most of the endocrine disrupters, pharmaceuticals and personal care products, with
the exception of lower molecular weight compounds [48,49]. However, incomplete rejection of certain
disinfection by-products, and some micropollutants of low molecular weight has been reported during
full and pilot scale high-pressure membrane applications [50]. Organic chemicals of high molecular
weight are effectively rejected by the MF/RO treatment, but those of low molecular weight (less than
500 Dalton) are less effectively rejected and have been detected in the RO permeate at low
concentrations [51]. However, the low molecular weight compounds detected in product water are present
in trace concentrations well below health significance.
As in drinking water treatment, the multiple barrier approach is also used in IPR. The approach
includes source control, use of multiple water treatment processes, use of environmental buffers and
Int. J. Environ. Res. Public Health 2009, 6
conventional drinking water treatment. The basis of this approach is to ensure that there are several
independent steps in place to remove contaminants given that no single barrier is able to remove all
contaminants from wastewater. The multiple barriers also minimize the risk by producing less
variation in the final water quality and by providing some protection in the event of poor performance of
one barrier, provided some degree of adjustment can be achieved in other treatment barriers to compensate
for temporary failures (e.g. disinfectant doses can be increased if membrane filtration underperforms).
Source wastewater assessment and protection is the first barrier and it is critical to prevent
contaminants from entering the wastewater. Source control requirements should be part of the formal
approval process to utilize recycled water for IPR as such requirements identify and minimize the
introduction of contaminants into the wastewater, minimising the need for them to be removed through
treatment. In Australia, the National Waste water Source Management Draft Guideline provides a
framework for good management of the quality and quantity of all wastewater source inputs to a
wastewater collection, transfer, treatment and disposal/reuse systems. The framework has been ordered
into five key wastewater input management objectives which cover the quality of all possible source
inputs with the potential to impact on sewage quality. These objectives address protection of safety in
sewers, infrastructure assets, treatment plants, regulatory compliance and recycling [52]. Therefore,
government agencies responsible for industrial wastewater control programs, as well as relevant
stakeholders, need to periodically review discharge permits, inspections programs, wastewater
monitoring plans, and enforceable discharge standards. Additional barriers beyond the advanced
treatment process include retention times in aquifers or surface waters as they act as an extra barrier, as
a buffer, to provide time to initiate corrective actions if required followed by drinking water treatment
before distribution to the community.
For the protection of human health, each treatment process must be evaluated to establish its
performance against the different categories of contaminants. A timely and effective monitoring
program is fundamental to detect the unexpected appearance of contaminants in the recycled water.
For example, additional treatment barriers after RO were implemented in the GRS (OCWD) project
after the detection of NDMA and 1,4 dioxane, both of which are potentially carcinogenic [29]. An
advanced oxidation process using hydrogen peroxide and UV radiation where added to break down
these contaminants and other potential undetected organic compounds [29].
4.3. Regulatory Framework
Different regions using IPR have developed various approaches to ensure health and environmental
protection. In the US, there are no federal regulations governing IPR and criteria are developed at the
state level. Therefore, states operating IPR projects, such as California, Washington, Arizona and
Florida, have each developed various guidelines. Criteria among states are generally similar and tend
to be conservative with an emphasis on maintaining protection of public health [53]. In California,
recycled water regulations for groundwater recharge of potable aquifers requires secondary treatment,
filtration, disinfection, and advanced wastewater treatment. Water quality goals, at that time, included:
pH 6.5-8.5; turbidity less than 2 nephelometric turbidity units; no detectable faecal coliforms; less than
1 mg/L chlorine residual, TOC less than 1.0 mg/L; and compliance with all drinking water standards
Int. J. Environ. Res. Public Health 2009, 6
[54]. In Florida, IPR projects have to meet drinking water standards: TOC less than 3.0 mg/L, total
organic halides less than 0.2 mg/L, and total nitrogen less than 10.0 mg/L [53,55].
Recycled water guidelines include both monitoring and performance requirements [56]. The
Department of Health Services, now the California Department of Public Health (CDPH) released the
first draft criteria for IPR via groundwater recharge in 1986. These guidelines revised in 2008 are
considered the most developed so far in the US, and include monitoring requirements related to
nitrogen compounds, unregulated emerging chemical contaminants (such as endocrine disrupters and
pharmaceuticals), and TOC limits [57]. The latest groundwater recharge reuse draft released by the
CDPH in August 2008, includes annual monitoring for endocrine disrupting chemicals and
pharmaceuticals. Some contaminants are listed in the Endnote No 5 of the Draft Guidelines, although
no specific indicator chemicals are recommended [58]. TOC requirement depends upon the degree of
recycled water recharged and should not exceed 0.5 mg/L divided by the proposed maximum recycled
water contribution [58]. CDPH is continually updating the guidelines as more information becomes
available. No doubt regulation will continue to evolve to address new issues or concerns as they arise.
Each project needs to select the contaminants to be included in its ongoing monitoring program based
on wastewater characteristics, treatment processes and risk assessments. Ongoing monitoring is
recommended to identify reliable indicator or surrogate chemicals. In 2007 the CDPH published a
Treatment Technology Report for Recycled Water identifying the recognized technologies that were
acceptable for compliance with treatment requirements [54]. RO is required for all IPR injection
projects and the minimum retention time in the aquifers is set at 12 months for direct injection and 6
months for infiltration of recycled water through soil.
Recycled water guidelines are now incorporating several approaches using a risk management
framework to ensure minimum levels of risk and maximum quality of the final product water. Best
Available Technology [59], Life Cycle Analysis and Hazard Analysis and Critical Control Points
(HACCP) [60,61] are some of the more commonly used approaches. The HACCP concept was
originally developed for risk management decisions involving health and safety in food and later used
in the pharmaceutical industry [62-64] and has been introduced for drinking water [60] and recycled
water [61,65,66]. The HACCP approach was used in the Australian Drinking Water Guidelines [67]
and in the National Guidelines for Water Recycling Phase 1 [68]. These latter guidelines include a risk
management framework and specific guidance on managing the health risks associated with the use of
recycled water for all applications other than potable use. The guidelines are intended to provide a
unified approach across Australia. The Phase 2 Guidelines for Water Recycling: Augmentation of
Drinking Water Supplies was released in May 2008 and they also follow a risk management approach
to ensure health protection [6].
The HACCP approach includes hazard identification and risk assessment, identification of
appropriate preventive measures, and operational monitoring of the preventive measures. The aim of
operational monitoring is to measure ongoing performance of preventive measures and to ensure that,
where required, corrective action is implemented prior to the water being released. In some cases,
monitoring can be continuous, whereas in other contexts, discrete sampling at lower frequencies is
employed. Because the efficiency of the treatment is variable and depends primarily on the quality of
the influent water the pressure of the water through the membranes, and the porosity of the membranes
Int. J. Environ. Res. Public Health 2009, 6
[69], a well-designed treatment process is essential to ensure adequate system reliability and
satisfactory operation over its lifetime.
Compliance testing alone is not enough to protect public health [70]. Firstly, it is not practical to
test for a large set of contaminants, as data gathering is costly in both time and resources. Furthermore,
analysis of the water quality is time-consuming and non-compliance with guideline values is always
detected after contaminated water has already been supplied; that is, it constitutes a “retrospective”
assessment. Many contaminants present at low concentrations are not directly or easily measurable.
Therefore, a coherent and structured evaluation of the hazards, and the management of the critical
control points plays a central role in the safe operation of recycled water projects. Consequently efforts
to protect public health should focus on failure detection systems that measure the performance of key
process units rather than just monitoring the final effluent or the end-use point. For example, the
parameters to identify failures in the performance of the MF and RO processes are generally indicated
by turbidity and conductivity respectively, that can both be monitored continuously using appropriate
plumbed-in instrumentation.
In summary, in order to conform to the HACCP management approach, very stringent water quality
and monitoring requirements are imposed for IPR. Typical requirements include advanced treatment of
the secondary effluent using MF/RO and in some cases also UV and/or advanced oxidation processes
to remove chemical and biological hazards, conformance with drinking water guidelines in the product
water, extensive monitoring for known or suspected contaminants, and minimum residence time in the
receiving aquifer or surface water body. Other requirements include monitoring and site-specific
controls on the operation, maintenance and management of the plants.
5. Knowledge Gaps, Aspects to be Implemented and Future Research
5.1. Recycled Water Quality, Monitoring and Risk Assessment
Analytical methods have been developed for a wide variety of compounds and isotopically labelled
standards have become commercially available in recent years. However, large-scale method
comparison and validation exercises to improve the accuracy and precision of quantitative
measurements have not yet been conducted. It is currently difficult to interpret and compare treatment
efficiency in the removal of emerging contaminants. More research is needed not only to identify new
potential contaminants of concern in recycled water, but also to develop validated methods and
implement harmonized analytical methods. Validated methods for emerging and other unregulated
contaminants will: (i) facilitate the risk assessment and regulatory process by providing better quality
data; (ii) provide comparative information about contaminant fate and removal during the treatment
barriers; and (iii) assist the analysis of different treatment options for removing contaminants. In 2005,
the 6th European Union framework funded the Norman Project, which aims to create a network of
reference laboratories and related organizations for chemical monitoring and biomonitoring of
emerging environmental pollutants [71-73]. In future years, it is expected that progress will be made in
the validation and standardization of chemical analysis and biomonitoring techniques for recycled
water relating to emerging pollutants.
Int. J. Environ. Res. Public Health 2009, 6
A greater research focus to manage health risks from trace organic compounds in recycled water is
needed, with a particular emphasis on investigating the toxicological relevance of endocrine disrupters
and pharmaceuticals in recycled water. The impact of endocrine disrupters in fish and other species
exposed to wastewater have been documented [74-76], but the implications of these findings for
human health remain inconclusive. There is also a need to develop approaches on recycled water
traceability that would permit attribution of the proportion of recycled water used in the context of risk
assessment and management studies. Given that it is not practical to test for a large set of chemicals of
concern, it is also essential to identify appropriate tracer or indicator compounds to follow their
occurrence and removal in the validation, verification and ongoing monitoring programs.
Validated monitoring approaches are required to ensure adequate health protection for a number of
reasons: (i) several unregulated chemicals of concern are not routinely included in monitoring
programs; (ii) many emerging chemicals of demonstrated or suspected health concern as yet have no
standard analytical methods; (iii) some current analytical methods have detection limits above the
toxic threshold; (iv) the possibility of other unknown toxic chemicals in the recycled water; and (iv)
combinations of toxic chemicals may exert mixture effects that remain poorly characterized.
Various monitoring approaches are available or in development, but are not in use with IPR
projects, include:
(1) On-line biomonitoring systems using fish have been developed in recent years to evaluate
potential health impacts without using concentrates of recycled water [77]. Behavioral and/or
physiological stress responses of organisms exposed in situ are evaluated, to provide additional
assurance that untested or as yet undetected chemicals of concern would not remain
(2) Biomarkers for endocrine, developmental, and potential reproductive effects in aquatic
organism exposed to recycled water are also under development and seem to be a promising
area [78].
(3) On-line sensor technologies for triggering contaminant warning systems have proven feasible
in the laboratory. For example, the USEPA studied 20 on-line commercial sensors for their
ability to identify 25 injected contaminants into the distribution system by testing of 17 water
quality parameters. They found that free chlorine and total organic carbon detected the widest
array of contaminants and produced the largest, and most easily detectable, water quality
changes [79]. However, more research is needed linking changes in physico-chemical water
quality indicators to the presence of contaminants relevant in the IPR context, and on the
sensitivity and long term reliability of online sensors (such as particle counters).
(4) Quantitative structure activity relationship (QSAR) methods are being used not only to predict
the potential toxicity of compounds based on their physical and chemical properties [80,81] but
also to predict rejection of micropollutants such as pharmaceutically active compounds by
different types of membranes during IPR treatment. This is a promising area that requires
further research.
Potential human health effects of previously untested contaminants may necessitate additional
regulations. It is fundamental to establish whether these emerging contaminants of concern may pose
an additional risk to human health at the concentrations reported in recycled water. A systematic
Int. J. Environ. Res. Public Health 2009, 6
approach is required to evaluate the measured concentrations of contaminants in recycled water against
benchmark values [6,82]. This approach may help regulators to identify contaminants that require
further health risk assessment or toxicological studies, as well as facilitating communication of study
findings in an effective manner to the community.
5.2. Regulatory Framework
Although many water authorities are aware of research into the various treatments and contaminant
rejection fractions personnel must also be provided with ongoing training in the emerging technologies
in IPR. More research and reports are expected in the future regarding the operation of IPR projects
and the implementation of management systems, such as the HACCP approach. Moreover, monitoring
of parameters, both online, and in the laboratory will identify performance compliance and when
threshold values are exceeded enable emerging problems to be detected and corrective actions taken.
Separating drinking water from sewage was a major achievement in the conquest of infectious
diseases, and remains a challenge to be overcome in much of the developing world. Now with the
intentional and planned augmentation of drinking water supplies with recycled water, it is fundamental
to ensure that the community remains protected. Therefore, there is a need to integrate both recycled
water and drinking water at the regulatory level. It is not enough to rely on drinking water standards
and guidelines to ensure the safety of the recycled water. This may result in a modification to the
approach to dealing with emerging contaminants in regulation of traditional drinking water sources. It
is also possible that additional chemicals may need to be monitored at drinking water treatment plants
once recycled water is introduced to the source water catchment. It is expected that with the
continuous development of treatment technologies, analytical methods, monitoring techniques,
toxicological studies and risk assessment approaches, the use and regulation of recycled water for IPR
will continue to evolve.
5.3. Epidemiological Surveillance
Regulators approving IPR projects need to implement a well-coordinated public health surveillance
system to document possible warning signs of any adverse health events associated with the ingestion
of recycled water. Existing surveillance systems, such as those for notifiable communicable diseases,
should be used and/or enhanced to meet these needs. Surveillance systems must be jointly planned and
operated by health departments, water utilities and other relevant agencies. Key individuals in each
agency need to be appointed to coordinate planning and rehearse emergency procedures. The
surveillance plan, its purpose, the monitoring results, and the system process performance should be
available to the community and interested stakeholders. Surveillance systems may indicate whether an
epidemiological study is required. However, epidemiological surveillance is considered relatively slow
and is reactive as it is based on disease outcomes.
In addition to the health surveillance program, the research capacity in regions considering IPR
needs to be enhanced to implement a monitoring program that provides an early warning system of
potential health risks from newly detected or emerging contaminants. In order for monitoring systems
to be effective, a multi-institutional commitment is required for the documentation and monitoring of
Int. J. Environ. Res. Public Health 2009, 6
all significant chemical wastewater inputs from household, commercial, agricultural and industrial
sources. Pre-established risk mitigation measures also need to be in place.
5.4. Public Perception
Although communities have accepted recycled water for non-drinking purposes such as irrigation of
parks, they are less likely to accept the use of recycled water as a drinking water source. The perceived
decrease in temporal and geographical distance between wastewater and recycled water in IPR raises
reservations amongst the community about the safety and quality of the recycled water. Emotions, or
the 'yuck' factor, play a major part in people’s lack of acceptance. Nevertheless, increased community
support has occurred in the last decade and important progress has occurred in identifying factors of
success or failure in the implementation of IPR projects [83-85]. Five aspects were identified by the
Water Environment Foundation for building and maintaining community support in recycling projects:
“(1) managing information for all stakeholders; (2) maintaining individual motivation and
demonstrating organizational commitment; (3) promoting communication and public dialogue; (4)
ensuring a fair and sound decision-making process and outcome; and (5) building and maintaining
trust” [83]. Promoting communication and public dialogue, and building and maintaining trust have
also been identified as key aspects in other studies [86-88].
Effective communication between the community, key stakeholders and the project proponent is
crucial to achieve community support. All recycled water projects need to be accompanied by
community education to demonstrate that the current technology is adequate to protect human health.
A timely and active communication program to discuss the treatment processes, the risks, the measures
in place to control risks and the safety of the water, may help to increase trust in the project. The
experience in the US has indicated that community understanding and acceptance may take several
years, but that a broad community communication approach is fundamental for the successful
implementation of IPR projects. There are many examples where local communities have rejected IPR
proposals because they were poorly informed or insufficiently confident in the process. Some
examples include the Dublin San Ramon Services District in California [9,85] and the Water Futures
Toowoomba in Queensland [17], where there was a lack of coordination between the authorities
involved in planning, health, water supply and environment, and/or inadequate community
consultation on the issue.
Community attitudes to water recycling are dependent on numerous factors, including the degree of
water scarcity, the supply costs, the quality of the consultative processes, the perceived management of
health risks, and the accountability of, and trust in, the regulator, the government and the water utility.
Therefore targeted social research is needed in communities where IPR is proposed to understand the
influence of psychological factors related to: perception of risk, motivations, attitudes, beliefs and
behavior on the use of recycled water to supplement existing water supplies and IPR project
Int. J. Environ. Res. Public Health 2009, 6
6. Concluding Remarks
IPR has been in practice for over 30 years. The projects presented have used advanced treatment
technologies and applied the treated recycled water into an environmental buffer where naturalisation
and dilution occur. Although few epidemiological studies have been conducted, there is no conclusive
evidence that communities using drinking water supplemented with recycled water are at any
increased risk of disease compared with those who do not drink recycled water.
IPR is a viable option for supplying reliable potable water to those urban regions with increased
water demand and/or decreasing alternative supplies. The use of IPR needs to be evaluated in
conjunction with other potential water supply alternatives, and the potential health impacts need to be
carefully considered before implementation. This process requires an understanding of how water
quality and health standards can be maintained through rigorous controls and monitoring techniques,
based on sound science and proven treatment technologies. IPR projects need to demonstrate
effectiveness of available barriers, guarantee safety by on-line monitoring systems, process control,
testing, and source control programs.
No water treatment is ever without risk, including conventional drinking water treatment and
traditional drinking water sources. Similarly, IPR as a new water source will never be a totally risk-
free practice. However, using best available technologies, risk assessment and risk management
practices, water agencies, health regulators and other stakeholders can evaluate and mitigate the
potential public health risks from the biological or chemical contaminants found or likely to be found
in the recycled water. Mitigation of hazards to their acceptable risk is critical to balance public health
protection and resources. Risk reduction below the acceptable risk will not result in significant
reduction in risk and at the same time additional expenditure of resources will not result in significant
advances towards increased safety.
It is essential to maintain ongoing research in hazard mitigation and control in IPR projects, coupled
with appropriate toxicological and epidemiological studies. The reviewed literature supports the
practice of IPR as a reliable and safe addition to existing drinking water supplies, and it is anticipated
that IPR will represent an essential element of sustainable urban water resources management in many
more regions of the world in the future.
This research was supported by the Western Australia Sate Government through the Premier’s
Collaborative Research Program (PCRP). The PCRP is a collaborative effort between: Department of
Health, Department of Water, Department of Environment & Conservation, Water Corporation, The
University of Western Australia, Curtin University of Technology, Chemistry Centre WA and National
Measurement Institute. State government funding was provided by the Office of Science & Innovation.
The authors thank Dr. Kathryn Linge from Curtin University for providing comments to the paper.
Int. J. Environ. Res. Public Health 2009, 6
Table 1. Demonstration and full scale potable reuse projects.
Project Place Year Treatment Buffer Population % Blended Comments Source
County Water
Water Factory
1975 -
Lime clarification,
filtration, granular
activated carbon,
filtration and
RO added in 1977.
Advanced oxidation
with hydrogen
peroxide and UV
added in 2001
Aquifer Less than 2
3.2% total
OC water
4.8% OC
Full-scale project Water
Factory 21 was built in 1975
and decommissioned in
First project that used
recycled water to maintain a
seawater intrusion barrier.
More than half the injected
water flows inland and
augments potable water
supplies. The injected water
reaches the nearest drinking
water bore after 2 to 3 years.
Addition of RO in 1977
enabled injection of up to
50% of recycled water.
system (GRS)
(Upgrade of
the Water
Factory 21
2004 to
MF/RO and
advanced oxidation
(UV and hydrogen
Aquifer 2.3 million
(300,000 to
by 2020).
15 - 18% Demonstration project
conducted before
construction of the GRS
plant produced 5 mgd. Full
scale plant produce 70 mgd
per year (10% of Orange
County's drinking water
Initially 75% of the recycled
water injected, later 100%
The groundwater basin
supplies more than half of
the population water needs.
Int. J. Environ. Res. Public Health 2009, 6
Table 1. Cont.
Project Place Year Treatment Buffer Population % Blended Comments Source
Potable Water
1985 -
Treatments tested
included: high-pH
lime clarification,
filtration, selective
ion exchange for
ammonia removal,
UV irradiation,
activated carbon
adsorption, RO, air
ozonation, chlorine
ultrafiltration and
NA NA NA The project investigated
different options for
alternative water supplies
and concluded that potable
reuse is a viable option.
Pilot plant used
unchlorinated secondary
effluent from the Denver
Wastewater Treatment Plant.
West Basin
Water District
MF/ RO UV and
advanced oxidation
Aquifer 950,000 10-15% Full scale project which
produces three types of
tertiary treated recycled
water for industrial and
irrigation uses, and three
types of RO water. Softened
RO water for groundwater
recharge, Pure RO water for
low pressure boiler feed, and
ultra-pure RO (which has a
second pass RO) water for
high pressure
Ground water recharge
represents 22% of the total
production. About 75% of
the recycled water injected
Lime clarification
Flow equalization
Sand filtration
Granular activated
Ion exchange
Post carbon
1.2 million 10 – 45 %
Full-scale project. Supplies
about 50% of the
population’s water supply.
During drought periods
recycled water provides up
to 90% of the reservoir
Recycled water is monitored
by an independent water
monitoring agency and is
considered the most reliable
source of water in the
Occoquan system.
Int. J. Environ. Res. Public Health 2009, 6
Table 1. Cont.
Project Place Year Treatment Buffer Population % Blended Comments Source
chloramination and
Inert media
filtration was added
in 1977 as an
additional measure
for public health
protection to
enhance virus
Aquifer 1.28
18.7% up
to 35%
Full-scale project
comprising three plants
located in the central basin
of Los Angeles County.
Whittier Narrows WRP
(built 1962) serves approx
150,000 people. The San
Jose Creek WRP (built in
early 1970s) serves 1
million and Pomona WRP
(built in early 1970s)
serves 130,000 people.
The recharged water is
composed of recycled,
storm and imported waters.
Injection of up to 50%
recycled water is
acceptable in any given
year providing that the
running three year total
does not exceed 35% of the
recycled water.
Tampa Water
1987 -
Pre-aeration, lime
gravity filtration,
and ozone
Granular activated
carbon, RO, and
ultrafiltration, were
also evaluated after
filtration and before
NA NA Demonstration project to
evaluate the treatment
efficacy of four advanced
water treatment processes.
Augmenting the reservoir
with recycled water from
the Howard F. Cullen
WWTP through the Tampa
Bypass Canal was selected
as the optimum system.
San Diego
1981 In 1985 Several
treatments tested
including RO and
granular activated
Since 2002
MF/RO, and
advanced oxidation
using UV light and
hydrogen peroxide.
NA NA Demonstration project
between 1985-1999 and
since 2002 full-scale
project for non-potable
reuse only due to
community opposition.
Health effects study
conducted in 1985.
Int. J. Environ. Res. Public Health 2009, 6
Table 1. Cont.
Project Place Year Treatment Buffer Population % Blended Comments Source
D.C. (USA)
1980 -
filtration, granular
activated carbon
adsorption and
Estuary NA NA Two years demonstration
The EEWTP influent water
was 50% recycled water and
50% estuary water.
The EEWTP blended water
treated with conventional
drinking water process
(such as: flocculation,
sedimentation and
disinfection) followed by
granular activated carbon
and chlorination.
1985 Two-stage
powdered activated
carbon treatment,
lime treatment,
recarbonation, sand
ozonation, GAC
chlorination, and
Aquifer 250,000 40 – 100% Full-scale project.
1997 MF UV Reservoi
1.7 million 8-12% Recycled water discharged
into the Chelmer river
which is used to augment
the Hanningfield reservoir.
The reservoir storage time
is up to 214 days
Monitoring of viruses and
estrogens since 1996.
Hormones in reservoir
<LOD of 3 ng/L
n Study
Singapore 2000 Ultrafiltration, RO,
UV, Stability
control and
4.4 million Currently
1% and
2.5% by
Initially a demonstration
plant, but has operated as a
full-scale plant since 2002
when adoption for
augmentation of drinking
water supplies was
Full-scale project with 3
existing plants. Total
production of 92 ML/day
from 3 plants. The majority
of recycled water is used
for industry.
Int. J. Environ. Res. Public Health 2009, 6
Table 1. Cont.
Project Place Year Treatment Buffer Population % Blended Comments Source
Project supported by a well
designed community
education program.
n Plant
1968 –
Algae flotation
Sand filtration
Granular activated
Pre-ozonation for
Fe/Mn removal
Dissolved air
Sand filtration
Granular activated
Sometimes used for direct
potable reuse.
Reuse Plant
2002 MF/RO + UV
Aquifer 60,000 40% Full-scale project that
produces between 40 to
50% of the drinking water
demand. The minimum
retention time in the
aquifer is 40 days.
Reported improvement in
drinking water quality with
lower hardness and better
color due to decreased
organic content.
Year: year project started; % blended: % of recycled water blended with alternate sources; Population: population served in the
distribution area
Int. J. Environ. Res. Public Health 2009, 6
Table 2. Epidemiological studies direct and indirect potable reuse projects.
Project Aim of the study Study
Experimental Details Results Source
Study No 1
Assessment of
health outcomes
between the
Forebay area,
which has received
some recycled
water in its water
supply with a
control area.
1969 -
Descriptive, ecological study
of more than a million
Four recycled water
exposure categories (high,
low and two control groups),
although the variable
proportion of recycled water
in the study area led to issues
of exposure
Three time periods
compared: 1969-1971, 1972-
1978 and 1979-1980.
The study did not account for
several confounding factor
The Scientific Advisory
Panel in 1986 concluded that
cancer outcomes were
inconclusive due to high
mobility of the population
and long latent period for
human cancers.
The short and long term
effects studied included
mortality, infectious
diseases, adverse birth
outcomes and cancer
An additional household
survey in 1981 interviewed
2523 women for information
on reproductive outcomes
and water consumption.
The population ingesting recycled
water did not demonstrate any
measurable adverse health effects.
However, the Scientific Advisory
Panel in 1986 concluded that
cancer outcomes are inconclusive
due to high mobility of the
population and long latent period
for human cancers.
The household survey found no
differences on specific illnesses or
measures of general health
between participants living in
high and low recycled water
areas. No association were found
for low birth weight, infant
mortality or congenital
Int. J. Environ. Res. Public Health 2009, 6
Table 2. Cont.
Study No 2
Assessment of
health outcomes
between the
Forebay areas,
which has received
some recycled
water in its water
supply for almost
30 years, with a
control area.
1987 -
Ecological study of a
population exposed to
between 0 and 31% recycled
water over a 30-years (1960-
Five exposure categories
(four groups receiving
increased percentages of
recycled water and one
control group) although
variable proportion of
recycled water in the study
area with issues of exposure
No evidence that recycled water
has an adverse effect on cancer
incidence, mortality and
infectious disease outcomes.
Significantly higher incidence rate
of liver cancer in the area with the
highest percentage of recycled
water was observed. However, due
to limitations of the study and the
lack of dose-response trend the
authors conclude that the results
are more likely explained by
chance or unaccounted
confounding variables.
Project Aim of the study Study
Experimental Details Results Source
Multivariate Poisson
regression used to generate
rate ratios.
The study did not account for
many confounding factors
Assessment of
adverse health
outcomes among
live born infants,
including low birth
weight, preterm
births, infant
mortality and 19
categories of birth
A cohort study that extended
the original reproductive
outcomes conducted in 1981.
Exposure group allocation
based on the average annual
percentage of recycled water
in water supplied by the
systems serving the ZIP-
code. Place of residence was
used as surrogate measure
for exposure which may
over-estimate or sub-estimate
the true exposure scenario
and no data on individual
exposure was collected.
High population mobility
may decrease the validity of
the results.
The study did not account for
several confounding factors
such as smoking or alcohol
consumption but is assumed
to be equal between the
recycled water and control
The study does not provide
evidence of an association
between recycled water and
adverse birth outcomes.
Rates of adverse outcomes were
similar in groups receiving high
or low percentages of recycled
Int. J. Environ. Res. Public Health 2009, 6
Table 2. Cont.
Reuse Project
Assessment of
cases of diarrhoeal
diseases, jaundice,
and deaths in
Windhoek, where
the average
contribution of
recycled water to
the waster was 4%
between 1968 and
An ecological study of 3000
deaths, excluding pre-natal
and unnatural causes of
Deaths were classified by
cause and race.
Windhoek statistics were
compared to global statistics
because Namibian data was
not available.
No association between any of the
studied health outcomes and
drinking water source was found.
* Diarrhoea was associated with
socio-economic status but not
with the recycled water.
Int. J. Environ. Res. Public Health 2009, 6
Table 3. Toxicological studies indirect potable reuse projects.
Project Aim of the study Experimental Details Results Source
County Water
District. Water
Factory 21
Santa Ana
River Water
Quality and
Health Study
Task No 7)
Water quality
evaluation and risk
assessment of Santa
Ana River, imported
water and recycled
water from Water
Factory 21.
At the time of the
study more than 90%
of the base flow of the
Santa Ana River
comprises wastewater
discharge which is the
primary source for
recharging the
groundwater basin
The relative risks to human health
associated with the three water
sources (Santa Ana River, imported
water or recycled water) were
compared using the USEPA
drinking water guidelines.
Quantitative relative risk
assessment methods used to
compare the water sources.
Estimates of the relative risk to
human health associated with each
water source were calculated.
For the microbial assessment it was
assumed that each water source was
consumed directly before being
used to recharge the groundwater
Risk assessment was reviewed by
an independent Scientific Advisory
Panel to assess the Santa Ana River
Water Quality and Health Study in
1996. The Committee agreed with
the report’s conclusions and
concluded that the health risk
associated with the quality of the
recycled water will be equal or less
than the other two water sources
Most of the organic carbon in the river
and recharge basins is of natural origin
and no chemicals of wastewater origin
were identified at concentrations of public
health concern. Anthropogenic dissolved
organic carbon (20-25% of total DOC)
consisted mostly of detergents and
None of the three water sources posed
significant non-carcinogenic risk to public
health and the risk posed by recycled
water was lower than the other sources.
Similarly the carcinogenic risk associated
with direct consumption of recycled water
was lower than the associated with the
other sources.
NDMA and 1,4-Dioxane are the
constituents that present more
carcinogenic risk in recycled water, while
NDMA at an assumed maximum
concentration of 20 ng/L presented the
highest carcinogenic risk.
Water produced by MF/RO treatment was
safe for consumption and actually
improved the groundwater basin’s water
Recycled water at the point of recharge is
projected to pose much less of a risk for
bacteria, parasites and virus than the other
water sources as long as all unit processes
in the treatment are operating properly.
Arsenic is the analyte that accounts for the
majority of risk in all water sources.
Denver Potable
Chronic toxicity and
oncogenicity studies
in animals.
Toxicological studies evaluated:
clinical observations, survival rate,
growth, food and water
consumption, haematology, clinical
chemistry, urinalysis, organ
weights, gross autopsy and
histopathology of major tissues and
Fischer 344 rats and B6C3F1 mice
were exposed to 150-fold and 500-
fold recycled water concentrates for
up to 2 years. Sprague-Dawley rats
were used for reproductive studies.
Clinical pathology, gross pathology, and
microscopic pathology conducted at
weeks 26 and 65 and at the end of the
study did not reveal any differences that
could be considered to be treatment
No adverse health effects were detected
from lifetime exposure to any of the
samples and during a two-generation
reproductive sample.
[100, 101]
Int. J. Environ. Res. Public Health 2009, 6
Table 3. Cont.
Project Aim of the study Experimental Details Results Source
Orange County
Water District
GWR system
On-line biomonitoring
of fish to evaluate the
water quality.
Shallow ground water originating
from the Santa Ana River
(approximately 85% of the river
base flow comes from recycled
water) and constituted control water
compared in a 9 months experiment.
Japanese medaka used as
Recycled water and treated recycled
water with granular activated
carbon were also compared in a 3
months experiment.
No statistically significant differences in
gross morphological endpoints, overall
mortality, gender ratios histopathology or
reproduction were observed in the 9
month study.
* In the 3 months experiment
reproduction and exposure to bio-
available estrogenic compounds was
evaluated with no significant differences
observed between treatments.
Denver Potable
Chronic toxicity and
oncogenicity studies
in animals.
Clinical observations, survival rate,
growth, food and water
consumption, haematology, clinical
chemistry, urinalysis, organ
weights, gross autopsy and
histopathology of major tissues and
organs were evaluated.
Fischer 344 rats and B6C3F1 mice
were exposed to 150-fold and 500-
fold recycled water concentrates for
up to 2 years. Sprague-Dawley rats
were used for
reproductive/teratology studies.
Clinical pathology, gross pathology, and
microscopic pathology conducted at
weeks 26 and 65 and at the end of the
study did not reveal any differences that
could be considered to be treatment
No adverse health effects were detected
from lifetime exposure to any of the
samples and during a two-generation
reproductive sample.
Denver Potable
Water quality
Organic challenge
Recycled water was compared with
the drinking water.
Fifteen organic compounds were
dosed at approximately 100 times
the normal levels found in the reuse
plant influent.
The recycled water quality was better
than the Denver drinking water for all
chemical, physical, and microbial
parameters tested except for nitrogen, and
alternative treatment options were
subsequently implemented for nitrogen
Challenge study demonstrates that the
multiple-barrier process can remove most
of tested contaminants to non-detectable
RO effluent met drinking water standards
for all pathogens sampled, but failed to
meet drinking water standards for a few
Hueco Bolson
Water quality
Routine sampling program
Bacteriological tests have shown an
average total of zero coliform per 100 mL
of effluent water.
The existing priority pollutant monitoring
of the injection well system has detected
only trihalomethanes, at levels below the
USEPA limit of 100 µg/L
Int. J. Environ. Res. Public Health 2009, 6
Table 3. Cont.
Project Aim of the study Experimental Details Results Source
(Health Effects
Characterization of
water quality for
microbiological and
inorganic chemical
Toxicological and
chemical studies to
isolate and identify
organic constituents of
significance to health.
Five year study starting in 1978
called Health Effects Study
compared the quality of
groundwater, recycled water, storm
water and imported water.
Ames Salmonella test and
mammalian cell transformation
assay were performed on all waters
as well as recycled water
concentrate 10,000 to 20,000 times,
with subsequent chemical
At the time of the study
approximately 16% of the injected
water was recycled water.
Concentrations of industrial organics and
metabolic by-products such as
phthalates, solvents and petroleum by-
products were higher in recycled and
storm waters but below EPA standards.
No relation was observed between % of
recycled water in wells and observed
mutagenicity of residues isolated from
The proportion of recycled water
currently used for replenishment had no
measurable impact on either groundwater
quality or human health.
None of 174 samples tested positive for
Only 10% of the organic matter
contained in the recycled water could be
Mutagenic activity using Ames test and
Salmonella tester strains (TA98 and TA
100) was detected in 43 of 56 samples
tested, including at least one from each
source, and was attributed to chlorinated
compounds. The level of mutagenic
activity (in decreasing order) was storm
runoff > dry weather runoff > recycled
water > ground water > imported water.
Health Effects
Water quality and
toxicological studies.
NeWater was compared to raw and
drinking water in the water quality-
monitoring program in which more
than 190 physical, chemical and
microbiological parameters were
The mice strain (B6C3F1) was used
for chronic toxicity and
carcinogenicity. Mice were fed for
up to 2 years with 150x and 500x
concentrates of NeWater and
reservoir water.
* A year-long fish study conducted
to assess long-term chronic toxicity
and estrogenic effects using the
orange-red Japanese medaka fish.
All tested parameters were below WHO
and USEPA drinking water guidelines
and standards for both NeWater and
drinking water.
The 3 and 12 month results indicated that
exposure to concentrated recycled water
did not cause any tissue abnormalities or
health effects. The 24 months results
remain unpublished.
No estrogenic or carcinogenic effects
reported in the fish studies.
Int. J. Environ. Res. Public Health 2009, 6
Table 3. Cont.
Project Aim of the study Experimental Details Results Source
San Diego
Water quality
Twenty-nine endocrine disrupter,
pharmaceuticals and personal care
products tested. Triclosan detection
after advanced oxidation was
possible due to bottle
Low-level concentrations of
trihalomethanes were detected below
drinking water standards. Eight of 29
emerging contaminants were detected
after RO but only triclosan remain after
advanced oxidation.
Tampa Water
(Health Effects
Characterization of
water quality for
chemical, physical
and microbiological
Toxicological testing
Recycled water quality was
compared to raw water from the
Hillsborough River. Raw water was
disinfected with ozone before
analysis to make it more analogous
to the recycled water.
Toxicological testing of recycled
water produced from 4 different
processes was compared in 1992.
Toxicological testing used up to
1000x organic concentrates used in
Ames Salmonella, micronucleus,
and sister chromatid exchange tests
in three dose levels. In addition a 90
day sub chronic assay and
developmental studies were
performed on mice and rats, and
reproductive toxicity was studied in
mice only.
In vivo testing included mouse skin
initiation (SENCAR mice initiation-
promotion studies) and strain A
mouse lung adenoma.
The recycled water did not present
significant microbiological or
toxicological risks.
Viruses were detected in 6.7 % of the
samples after chlorination, but this
occurred during an operational period
when pH levels were suboptimal.
Mutagenic activity tested using
Salmonella/microsome assay was
positive but no significant positive
response was observed in vivo.
All tests were negative for
developmental toxicity, except for some
foetal toxicity exhibited in rats, but not
mice, for the advanced water treatment
A panel of six internationally recognized
water quality and health effects experts
comprised a Health Effects Group that
concluded recycled water is safe for
human consumtion.
San Diego
(Health Effects
characterization and
quantification of
infectious diseases
agents and potentially
toxic chemicals.
Screening for
mutagenicity and bio-
accumulation of
chemical mixtures.
Chemical risk
Study compared the genetic effects
of recycled water and the existing
raw water supply.
150-600x organic concentrates were
used in Ames Salmonella test;
micronucleus, 6-thioguanine
resistance, and mammalian cell
transformation testing were
Biomonitoring experiments using
fathead minnows and fish to
evaluate survival, growth,
swimming performance and
chemical bio-accumulation
The average total organic carbon
concentration was 1.37 mg/L in the
recycled water and 9.83 mg/L in the raw
water. Similar inorganic species were
found in samples from both waters,
although there was greater evidence of
bio-accumulation from raw water.
The Ames test showed some mutagenic
activity, but recycled water was less
active than drinking water. The
micronucleus test showed positive results
for both waters but only at the high
(600x) doses than for raw water.
Int. J. Environ. Res. Public Health 2009, 6
Table 3. Cont.
Project Aim of the study Experimental Details Results Source
Trace amounts of 68
base/neutral/acid extractable
organics, 27 pesticides, and 27
inorganic chemicals were tested in
fish tissues after exposure.
In vivo fish biomonitoring (28-day bio-
accumulation and swimming tests)
showing no positive effects. Recycled
water and raw water were only
distinguishable in 28 days chemical bio-
accumulation tests for pesticide levels,
which were higher in raw water. Better
performance of fish survival, growth,
and swimming performance after 90 and
180 days exposure in the raw drinking
water may be related to ionic
There was no significant health risk from
non-carcinogenic chemicals in either
water. The chemical risk estimates were
dominated by bis(ethylhexyl)phthalate in
recycled water and by arsenic and
trihalomethanes in the raw water. The
risk from human intake of recycled water
was 40 times lower
Toxicological studies Water quality achieved from the
blending of 50% recycled water
after secondary treatment and 50%
Potomac estuary water was
compared with drinking water.
Ames Salmonella test and
mammalian cell transformation
assay were conducted using organic
concentrates of 150-fold.
* The NRC report did not support
the study conclusion due to few
toxicological studies conducted.
Recycled EEWTP water had less
mutagenic activity (the effluent tested
positive only about 10 percent of the
time) than the drinking water by the
Ames test. The cell transformation
assays also tested positive for both
waters with similar small numbers of
positive results.
The study concludes that the treatment
produce a water quality acceptable for
human consumption, although the
National Research Council report did not
support the study conclusion due to the
limited number of toxicological studies
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... Water has been regarded as an abundant and inexhaustible resource. However, only 2.5% of the Earth's water constitutes freshwater [21], which is vital for the survival of various species, while a mere 0.3% is available for human consumption [21]. The accessibility of freshwater is severely restricted due to a combination of factors, including population growth, overuse, pollution, and constant withdrawals [22]. ...
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Chlorination/dechlorination and advanced disinfection processes (UV irradiation, ozonation, membrane filtration) have been reviewed in terms of their efficiency, regrowth potential, design parameters, experimental set-up, scale-up and industrial experiences. Existing results show the great influence of water quality, in particular of suspended matter concentration and organic content. The efficiency and reliability of these processes are evaluated for different reuse applications. The critical analysis of the literature data and experimental results highlights UV irradiation as an effective and competitive advanced disinfection process. Ozonation is a viable solution in case of higher requirements for water quality including virus and protozoa removal. Ultrafiltration is a highly efficient process producing an excellent quality and totally disinfected effluent, particularly recommended for groundwater recharge and potable wastewater reuse. The choice between these advanced disinfection technologies depends on wastewater quality, existing standards, specific reuse applications and wastewater treatment work capacity.
During the late 1980's and early 1990's the City of San Diego built and operated a 1,900 m3/d (0.5 Mgal/d) wastewater pilot facility to evaluate the efficacy of a unique combination of treatment methods for the reclamation of wastewater to a quality acceptable for human consumption. The primary objective of the study was to investigate if the City's advanced wastewater treatment system could reliably reduce the contaminants of concern to levels such that the health risks posed by an assumed potable use are no greater than those associated with the present water supply. The results of this substantial research effort indicated that the processes involved can reliably produce a water of equal or better quality than that of the present raw water supply.
In 1968, a direct water reclamation system from domestic sewage was pioneered in Windhoek, Namibia, to supplement the potable water supply to the city. This system went through a succession of modifications and improvements over the years, but consistently produced water of acceptable quality, as evidenced a comprehensive chemical, bacteriological, virological, and epidemiological monitoring. Now, in 1995, Windhoek is again facing a shortfall of potable water in the light of a population increase (growing at 6% to 8% per annum) and increasing water demand, and is currently extending the water reclamation system from the previous 4800 to 21000 m3.d−1, the maximum attainable. All the components of the reclamation system are being reviewed and re-analyzed; demand management, diversion of some industrial effluents, wastewater treatment, water reclamation, oxidation and adsorption technologies, blending of reclaimed wastewater with other sources, buildup of salinity, treatment costs, and monitoring and quality control strategies. The practical experience at Windhoek demonstrates that a direct wastewater reclamation system is a practical, responsible way of augmenting potable water supplies in arid regions, but that it requires comprehensive planning, training and on-going commitment for its continued success.
Water reuse is well established in the United States, with uses ranging from pasture irrigation using reclaimed water that has received a low level of treatment, to augmentation of potable water supplies with highly treated reclaimed water. There are no federal regulations governing water reuse and criteria are developed at the state level. Criteria differ between states that have adopted regulations or guidelines, but criteria among states where water reuse is prevalent are similar and tend to be conservative, with public health protection being the most important consideration. The US Environmental Protection Agency (EPA) has published guidelines for water reuse that include recommended criteria for various reclaimed water applications.
In the Netherlands interest in advanced treatment is increasing now that almost all wastewater treatment plants apply full biological treatment and nutrient removal. Membrane filtration of WWTP-effluent appears to be a very promising method to remove suspended solids and, in addition, bacteria and viruses. Experiments with a pilot unit consisting of a dual media prefilter and a membrane filter, containing capillary membranes with a pore size of 0.01 μm (ultrafiltration) and working in a semi dead-end mode, gave rather promising results. A flux of 90 l/m2.h was achieved after optimizing the cleaning procedures (TMP 0.6 bar, recovery > 90%). Experiments with microfiltration (transverse flow module) based on the cross-flow principle were successful only at high cross flow velocities (flux 100 l/m2.h, TMP 0.5 bar, recovery 80%). The ultrafiltrate showed an excellent quality with the absence of suspended solids and bacteria. Finally, low costs for energy (NLG 0.02/m3 (1 NLG = 0.5 US$)) and chemicals (NLG 0.01/m3) were calculated. Further optimization will facilitate the applicability of membrane filtration in the near future.
Tertiary treatment processes were tested to demonstrate their ability to produce effluents that meet the most stringent standards in the California Wastewater Reclamation Criteria. The processes studied were in-line, granular media filtration and microfiltration for particulate removal, and chlorination and UV light for disinfection. In-line filtration met CWRC turbidity requirements, although filter performance was dependent on feed water turbidity, and alum and polymer doses. Microfiltration produced an effluent virtually free of suspended solids and coliforms, and a 1.9-log removal of MS2 phage. This decreased the level of microorganism inactivation required of the UV system. MS2 phage sensitivity to UV light was not constant, which may question its suitability as an indicator organism to assess virus inactivation. Minimum chlorine Ct value of 340 mg.min/l, and UV dose of 800 J/m2 were identified for in-line filtration effluent, while a dose of 450 J/m2 was sufficient for microfiltration effluent. In-line filtration followed by UV disinfection is less costly for water reclamation than any other combination of treatment units tested, and, therefore, these processes were selected for a 53.000 m3/d water reclamation plant in San Francisco.
Natural replenishment of the vast supply of underground water occurs very slowly; therefore, excessive continued exploitation of groundwater at a rate greater than this replenishment causes declining groundwater levels in the long term and if not corrected, leads to eventual mining of groundwater. To increase the natural supply of groundwater, artificial recharge of groundwater basins is becoming increasingly important in groundwater management and particularly in situations where the conjunctive use of surface water and groundwater resources is being considered.
Hazard Analysis and Critical Control Points (HACCP) was applied for identifying and controlling exposure to pathogenic microorganisms encountered during normal sludge and wastewater handling at a 12,500 m(3)/d treatment plant utilising tertiary wastewater treatment and mesophilic sludge digestion. The hazardous scenarios considered were human exposure during treatment, handling, soil application and crop consumption, and exposure via water at the wetland-area and recreational swimming. A quantitative microbial risk assessment (QMRA), including rotavirus, adenovirus, haemorrhagic E coli, Salmonella, Giardia and Cryptosporidium, was performed in order to prioritise pathogen hazards for control purposes. Human exposures were treated as individual risks but also related to the endemic situation in the general population. The highest individual health risk from a single exposure was via aerosols for workers at the belt press for sludge dewatering (virus infection risk = 1). The largest impact on the community would arise if children ingested sludge at the unprotected storage site, although in the worst-case situation the largest number of infections would arise through vegetables fertilised with sludge and eaten raw (not allowed in Sweden). Acceptable risk for various hazardous scenarios, treatment and/or reuse strategies could be tested in the model.
Water reclamation and reuse is an established water resources management practice in the United States. Although many regulatory agencies do not advocate the use of reclaimed water for potable purposes, indirect potable reuse via groundwater recharge and surface water augmentation is occurring. Depending on the intended use of reclaimed water, factors such as health protection, user water quality and quantity requirements, irrigation effects, environmental effects, aesthetics, and public and/or user perception of the reuse concept may have to be considered.