Rain Water Harvesting in Urban Building

Full text

SECM/13/92
RAINWATER HARVESTING IN URBAN BUILDINGS
Gayani Karunasena1, Harshini Mallawaarachchi2 and J.D.E.M. Gunasekara3
1Department of building Economics, University of Moratuwa, Sri Lanka
Email: gayanik@uom.lk
2Department of building Economics, University of Moratuwa, Sri Lanka
Email:
1.0 Introduction
hmallawarachchi@gmail.com
3Department of building Economics, University of Moratuwa, Sri Lanka
Abstract
Scarcity of water for human needs is prevalent throughout the world today. Thus, many methods are
being suggested to increase water supply; one alternative being rainwater harvesting. Rainwater
harvesting is an ancient technique more popular worldwide because of its effectiveness. Sri Lanka has
a long history associated with rainwater harvesting. The recorded history of hydraulic civilization
dates back to 5th century B.C. Large number of reservoirs, tanks, dilapidated irrigation structures and
inscriptions stand testimony to the dynamics of our hydraulic civilization. To date, this traditional
technique is implemented island wide, especially in rural areas with the new name of rainwater
harvesting. However, to date there is very few rainwater harvesting systems implemented in urban
buildings. There is a need to develop rainwater harvesting systems for urban buildings as a solution
for water scarcity and high utility bills in urban buildings. Thus, this study aims to explore and
identify rainwater harvesting systems in urban areas and identify the factors that affect the effective
rainwater harvesting system. Comprehensive literature review was conducted for data collection and
professionals from both private and public sector involving rainwater harvesting were interviewed for
views on urban rainwater harvesting. The study revealed technical, economical, environmental and
operational factors that influence design and implementation of effective rainwater harvesting system.
The study enabled to explore the current status of the urban rainwater harvesting and highlights the
strengths and weakness of the identified factors for successful implementation of urban rainwater
harvesting system in Sri Lanka.
Keywords: Rainwater harvesting, Factors, Urban buildings, Sri Lanka
Rainwater harvesting is an ancient technique more popular worldwide which is suitable for all
building types and can be retro-fitted to existing buildings or integrated into new building designs
(Dwyer, 2008). Abdulla and Al-Shareef (2009, p.196) defined that “Rainwater harvesting is a
technology used for collecting and storing rainwater from rooftops, land surfaces, road surfaces or
rock catchments using simple techniques such as pots, tanks and cistern as well as more complex
techniques such as underground check dams”. According to as study by Cabell Brand Center (2009),
the economic feasibility of harvesting rainwater differs based on many factors, such as precipitation
frequency, water consumption needs, prices of local water and wastewater treatment, cost of
Special Session on Green Building, 4th International Conference on Structural Engineering
and Construction Management 2013, Kandy, Sri Lanka, 13th, 14th & 15th December 2013
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installation and maintenance. As water resources become more limited, use of rainwater as alternative
water resources has drawn attention (Kim et al., 2007).
According to National Water Supply and Drainage Board, the urban population of Sri Lanka is 31 %
of the total population of 19.0 millions, which amount to 5.9 million and expected to increase more
with increasing urbanization (Ariyananda, 2007). Same described that, the urban authorities find it
extremely difficult to expand their water supply schemes not only due to financial constraints but also
due to limited water resources. Rainwater harvesting techniques successfully used in rural areas offer
much hope in supplementing the conventional sources of water supply. There is only few rainwater
harvesting systems implemented in urban buildings (Ariyananda 2007). There is a need to develop
rainwater harvesting systems in urban buildings as a solution for water scarcity and high utility bills.
In this context, it is important to identify “how the rainwater harvesting systems are practiced in urban
buildings in Sri Lanka”. Thus, this study is to explore and identify the rain water harvesting systems
in urban buildings. This paper covers the concepts relating to rainwater harvesting, rainwater
harvesting practices in global and urban buildings in Sri Lankan context.
2.0 Literature review
2.1 Rainwater harvesting and its importance
Rainwater harvesting is an ancient technique enjoying a revival in popularity due to the inherent
quality of rainwater and interest in reducing consumption of treated water (Texas Water Development
Board, 2005). According to Paraghane et al.(2006, p.31) “Rainwater Harvesting is a system by which,
rainwater that collects on the roofs and the area around buildings is directed into open wells, bore
wells, tube wells through a filter tank or in to a percolation chamber, built specifically to serve the
purpose”. Further more rainwater harvesting implies collection and storage of the rainy season
precipitation that would have seeped into soil or run off into stream channels (Li et al., 2000). Abdulla
and Al-Shareef (2009, p.196) defined that, “Rainwater harvesting is a technology used for collecting
and storing rainwater from rooftops, land surfaces, road surfaces or rock catchments using simple
techniques such as pots, tanks and cistern as well as more complex techniques such as underground
check dams”.
Accordingly, Rainwater harvesting can be simply defined as a technology used for collecting and
storing rainwater by using simple techniques such as pots as well as more complex techniques such as
storage tanks to meet demand for water by human activities. Rainwater harvesting is suitable for all
building types and can be retro-fitted to existing buildings or integrated into new building designs
(Cabell Brand Center, 2007). According to Lawson (2009) and Cabell Brand Center (2007), collected
rooftop water can be used for non potable such as, household cleaning, industrial processing,
landscape irrigation, fire suppression and potable demands. Additional water treatment components
must be installed to treat rainwater to drinking water standards.
Thereby, the importance of rainwater harvesting make sure that, there is no water shortage in the
future and approach of rainwater harvesting system into the building is an effective way to minimize
the use of treated water for non-potable use. When consider rainwater harvesting systems, it has
numerous advantages. Rainwater which comes free is the purest form of water. The only cost is for
collection. As well as running costs is low (Lawson 2009). Rainwater also conserves energy as the
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energy input needed to operate a centralized water system is bypassed. This is of considerable
importance at a time when energy is becoming scared and expensive (Weeraratna et al., 2009).
2.2 Rainwater harvesting for urban buildings
The urban population of Sri Lanka is presently 31 % of the total population of 19.0 millions, which
amount to 5.9 million people and expected to increase more with increasing urbanization (Ariyananda
2007). Further same author described that it is predicted in the year 2025, that 60 % of Sri Lanka's
population of 23 million will be in urban areas. Recently the government legalized the adaptation of
rainwater in all new buildings in urban areas and this has opened many eyes towards rainwater
harvesting (Weeraratna et al., 2009). It is expected that in order to respond to the legal requirements,
there will be many requests for professional assistance to design rainwater harvesting systems to
buildings in the category of residential, commercial, industrial and institutional.
According to studies about 60 % of rainwater of urban areas flow in to sea and rainwater harvesting
can make use of this wasted water and also to certify the use of purified pipe borne water for
appropriate usages (Lanka Rain Water Harvesting Forum, 2009). Tanks can be used to collect water
for general use and wells and pit holes (surface runoff tanks) can be used to recharge the ground water
and ponds are used in large facilities such as factories and office complexes for collection of rain
water (Lanka Rain Water Harvesting Forum, 2009). Rain water harvesting in urban buildings has
many functions. Local erosion and flooding in urban areas during heavy rains are lessened as a
portion of local rainfall is diverted into collection tanks (Ariyananda 2007). Besides it minimize the
use of piped potable water for secondary purposes (Fernando 2007). In addition to that, purchase of
water from private and government sector unreliable in quality and is also expensive. Rainwater
harvesting avoid those problems (Weeraratna et al., 2009).
Further, same author stated that, collected water can be used during emergencies such as fire fighting
and when the centralized water is broken or being repaired. However, rainwater collected in urban
areas is not recommended for drinking and cooking due to the high level of air pollution, animal
droppings and dust in urban areas (Lanka Rain Water Harvesting Forum 2009).
2.3 Rainwater harvesting in Sri Lanka
Rainwater harvesting is accepted as a feasible water supply option in many countries and even in Sri
Lanka, potentiality in rainwater harvesting is well documented in the National Rainwater Harvesting
Policy (Ariyananda 2009). According to Lanka Rain Water Harvesting Forum (2009), especially in
rural areas which are vulnerable to periodic droughts, rainwater harvesting is a viable option for the
basic water needs. This water can be used for domestic use including drinking, cooking, washing and
also for the needs of agriculture. Weeraratna et al. (2009) clarified; domestic systems in rural areas
used the basic rainwater harvesting system to collect the rainwater. Lanka Rain Water Harvesting
Forum (2009) described that, there are two categories of storage tanks; namely, surface tanks and
subsurface tanks. closed surface tanks made of brick or cement which collect water from the roof top
are used to harvest water for domestic use and open tanks or wells (subsurface tanks) can be used to
collect the surface runoff water which can be used for agriculture and also for ground water
recharging.
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According to Lanka Rain Water Harvesting Forum (2009), 30282 numbers of rain water tanks are
established all over the country. According to Weeraratna et al. (2009), rainwater harvesting in urban
buildings has many advantages. Because of that Sri Lanka has given focus to implement the rainwater
harvesting in urban buildings (Lanka Rain Water Harvesting Forum, 2009). However, the future
prospect of rainwater harvesting in Sri Lanka depend on the adequacy of the tank size, quality of
stored water and proper operation maintenance of the rainwater harvesting system. It created an
importance to study about the application of rain water harvesting system and to develop a system for
urban buildings in Sri Lanka as a solution for water scarcity and high utility bills in urban buildings.
Accordingly, this study aimed to explore and identify rainwater harvesting systems in urban areas and
identify the factors that affect the effective rainwater harvesting system.
3.0 Research methodology
The study was conducted as a qualitative research as it needed detailed information and analysis and a
qualitative outcome. Hence, case study method was applied while two commercial buildings and two
industrial buildings were studied as a multiple case study approach. Semi structured interviews were
selected as data collecting source of the research due to its impotence and essentiality to the case
study approach. The interviews were conducted with key professionals involve in rainwater
harvesting in respective cases based on their experience. The collected data was analyzed using cross
case analysis.
4.0 Findings and analysis
Most essential environmental factor which was identified by all interviewees is rainfall characteristics
of the area. According Maintenance engineer of the Case C, the availability of rainfall data series in
space and time and rainfall distribution is important for rainfall-runoff process. According
Maintenance engineer of the Case A, “can compete with other water supply systems”. Case A and B
get respectively 2400 mm and 3000 mm annual rainfall”. Tropical climate with short dry seasons and
multiple high intensity rainstorms provide the most appropriate condition form rainwater harvesting.
When the dry period has raised water demand of the office building can accomplish by other water
resources, because of the unforeseen rainfall pattern. All the interviewees indicated that, water
demand of the organisation is a significant technical factor to implement a successful system. Case A
and B consumed respectively 75% and 50 % of rainwater from total water consumption. Rainwater
demand is differed according to water requirements of both cases. As mentioned by all interviewees,
design and implementation of both cases was out sourced; because lack of experience regarding water
harvesting. Rainwater catchment surfaces of Case A are roof top of the buildings (2,315 m2) and
ground area (1452 m3). Even though, Case B only designed the roof area (2842 m2). The Chief
engineer of Case B revealed that, “the selection of the catchment area is based on the rainwater
demand”. The rainwater harvesting system of Case A gets the advantage of 6.5 ha sloping of the site
to collect ground water. As the geology of the cistern site is important factor; when the rainwater from
the ground area.
A well-designed, carefully constructed, properly fitted and maintained and delivery system (gutters
and downpipes) is essential because the guttering is often the weakest link in a rainwater harvesting
system. The Chief engineer of Case A revealed that, “capacity of the storage tank is based on three
main criteria; area of roof, collection efficiency and depth of rainfall in addition to location and
material of storage tanks”. All the interviewees divulged that, since the harvested rainwater only used
for non potable water demand, it is unnecessary to use complex water treatment methods; because
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sand filters are only used. The interviewee of Case A stated that, all black and grey water of the
complex is recycled to a quality suitable for landscaping and gardening through network of septic
tank, central vertical flow filter with subsequent ponds. Water is pumped through a pressurized pump
system and dedicated system for use in toilet flushing and gardening in both cases. Both systems
require occasional maintenance for effective operation. The Environmental executive of Case D
specified that, “treatment process may differ according to rainwater demand, allocated budget for
water treatment and use of rainwater”. Allocated budget is the main economical factor that affect for
implementing the rainwater harvesting system. Cost of construction and cost of operation and
maintenance of both cases may differ according to water demand and technologies.
The harvested rain water of Case D is used for water cooling system of the AC system, gardening and
toilet flushing and other washing purposes. All interviews stated that, they faced difficulties in making
the workers understand the rainwater harvesting method and ignorance by the workers. It was
overcome by organizing awareness programmes. However, a successful rainwater harvesting system
should comply with the organisational conflict and policies and government regulations as essential
operational factor.
5.0 Discussion
According to the case analysis and findings, there are many factors affecting the implementation of
rain water harvesting system in urban buildings can be identified as follows.
According to the Table 01, the factors affecting rain water harvesting system can be identified as
technical; environmental; economical; and operational factors. The design, implementation, operation
and maintenance of a successful rainwater harvesting system shall be determined by these factors.
The decision maker has to balance the total cost of the system against the available budget, including
the economic benefit of conserving water supplied from other sources. The capital cost of rainwater
harvesting systems is highly dependent on the type of catchment, conveyance and storage tank
materials used. The capital saving from rainwater harvesting can calculated by considering utility bill
saving. Harvested rainwater of office complexes only used for non potable water demand as toilet
flushing, landscaping and vehicle washing. Harvested rain water of factory buildings are used for
water requirements such as landscaping; workers lunch rooms; workers bath rooms; toilet flushing;
workers urinals; fire fighting; watering lawn and garden; and production purposes such as cleaning
batteries before charging and water cooling system of the AC system. Because of that factory
buildings were applied adequate water treatment process to improve the quality of the rainwater. But
the office complexes only used primary water treatment methods such as sand filters. Because of that,
the rainwater treatment method depends on the use of harvested rainwater. Any of the selected case do
not utilize for drinking; because of the uncertainty regarding quality of rainwater and cost of water
treatment.
Their main problem while implementing was lack of experience and lack of facilities to train the
workers; because design and implementation of all cases were outsourced. Due to that, various levels
of governmental and community involvement in the development of rainwater harvesting
technologies is essential. Also, in factory buildings they faced another difficulty in making the
workers understand the rainwater harvesting method and ignorance by the workers. It was overcome
by organizing awareness programmes. Any successful rainwater harvesting system should comply
with organisational policies and government regulations.
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Table 1: Factors affecting rain water harvesting system
MAIN FACTORS
SUB FACTORS
Environmental Factors
Rainfall intensity, distribution and dry period
Quality of rainwater
Availability of other water resources
Impact on the environment
Technical Factors
Water demand
Type of the system
Use of the system
Availability of technologies
Catchment area
Run-off coefficient
Material, slope and type of roof
Delivery system
Capacity of the storage tank
Location of cistern
Geology of the cistern site
Water treatment methods
Economical Factors
Available budget
Cost of construction, Operation and maintenance
Reduction in utility bills
Operational Factors
Organisational policies
Government regulations
Safety of the system
Response of workers
6.0 Conclusions
Demand on water resources has increase day by day due to the population growth and expansion in
urbanization, industrialization and irrigated agricultural. Adopting the concept of sustainability and
conservation of water resources can help to cope with the global water shortage. Rainwater harvesting
system is one of the concepts that can be implemented to meet the water shortage problem. The
quantity and quality of rainwater collected is different from place to place depending on the weather,
geographic location, activity in the area and storage tank. Furthermore, rainwater has a lot of potential
as an alternative water resource for the future because of its high quality. Rainwater quality always
exceeds the surface water and comparable to ground water because of it does not come in contact with
soil and rocks where it can dissolve salts and mineral which is harmful for potable and non-potable
uses. Successful implementation of rainwater harvesting system is a great contribution for future
rainwater harvesting development and living quality.
When consider the future of rainwater harvesting technology. Rainwater harvesting presents an
opportunity for augmentation of water supplies allowing for self-reliance and sustainability. There is a
need for the water quality aspects of rainwater harvesting to be better addressed. Greater involvement
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of the public health department in the monitoring of water quality will affect the effective rainwater
harvesting systems. There should be a provision of assistance to the public in sizing, locating, and
selecting materials and constructing storage tanks, and development of a standardized plumbing and
monitoring code and promotion of rainwater harvesting as an alternative to both government and
private sector supplied water, with emphasis on the savings to be achieved on water bills.
Acknowledgement
The authors acknowledge assistance rendered by Head of Department, senior lecturers, lecturers and
other staff members of Department of Building Economics, University of Moratuwa. Researchers
express their gratitude to all practitioners in the industry who contributed to this study with many
helpful comments.
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