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Field trial of an automated batch chlorinator system at
shared water points in an urban community of Dhaka,
Nuhu Amin, Yoshika S. Crider, Leanne Unicomb, Kishor K. Das,
Partha Sarathi Gope, Zahid Hayat Mahmud, M. Sirajul Islam,
Jennifer Davis, Stephen P. Luby and Amy J. Pickering
Point-of-use water treatment with chlorine is underutilized in low-income households. The Zimba, an
automated batch chlorinator, requires no electricity or moving parts, and can be installed at shared
water points with intermittent ﬂow. We conducted a small-scale trial to assess the acceptability and
quality of Zimba-treated municipal water. Fieldworkers collected stored drinking water over a 10-week
period from control (n¼24 households) and treatment (n¼30 households) compounds to assess levels
of free chlorine and E. coli contamination. Overall, 80% of stored drinking water samples had a
safe chlorine residual among treatment households, compared to 29% among control households
(P<0.001). Concentrations of E. coli were lower (mean difference ¼0.4 log colony-forming units/
100 mL, P¼0.004) in treatment compared to control households. Fifty-three percent of mothers
(n¼17), thought the Zimba was easy to use and 76% were satisﬁed with the taste. The majority of
mothers mentioned that collecting water from the Zimba took more time and created a long queue at
the handpump. The Zimba successfully chlorinated household stored drinking water; however, further
technology development is required to address user preferences. The Zimba may be a good option for
point-of-collection water treatment in areas where queuing for water is uncommon.
Kishor K. Das
Partha Sarathi Gope
Zahid Hayat Mahmud
M. Sirajul Islam
Stephen P. Luby
International Centre for Diarrhoeal Disease
Research, Bangladesh (icddr,b),
Yoshika S. Crider
Stephen P. Luby
Amy J. Pickering (corresponding author)
Key words |automated chlorine dispenser, Bangladesh, chlorination, household water treatment,
urban, water quality
Each year, more than 800,000 children <5 years old, mostly
from low-income countries, die of diarrhea (Liu et al. ).
Evidence from randomized controlled trials suggests that
point-of-use (POU) water treatment with chlorine reduces
reported diarrheal disease (Fewtrell et al. ;Arnold & Col-
ford ;Clasen et al. ), but POU techniques have been
poorly adopted and inconsistently used among low-income
households (Rosa & Clasen ). Two major barriers to
uptake of POU technologies are the formation of new habits
and the amount of time required each day for water treatment
(Luby et al. ;Luoto et al. ). For example, one reason
for low adoption of POU chlorine technologies might be the
requirement to add chlorine each time drinking water is col-
lected, which requires personal motivation, knowledge and
behavior change. If these criteria are not met, inconsistent
and inaccurate chlorine dosage could result.
An additional limitation of current POU chlorination is
that treatment of varying batch sizes requires customized
dosage volumes (i.e., for 5, 10 or 20 L) (Clasen & Edmondson
;Kremer et al. a,b), and users may not know how
32 Research Paper © IWA Publishing 2016 Journal of Water, Sanitation and Hygiene for Development |06.1 |2016
to measure out different sized chlorine doses. There are lim-
ited options for low-cost, accessible water treatment for
larger (>10 L per day) quantities of water. Similarly, smaller
amounts (i.e., one glass or jug) are not easily dosed with the
same products used for more common larger collection
Because of the barriers to POU water treatment, manual
chlorine dispensers have been promoted to encourage house-
holds to treat their water at the time they collect it (Kremer
et al. a,b). Manual chlorine dispensers are designed
to add 3 mL of diluted chlorine to 10–20 L of water (depend-
ing on the concentration) with the turn of a knob. These
dispensers are installed next to communal water points
(Kremer et al. a,b). Manual dispensers have certain
advantages over POU treatments with liquid chlorine at the
household level (Lantagne ), since the dispenser provides
the correct dosing if the collection container is a standard size
(no need to measure chlorine) and also takes advantage of
peer-effects when installed at public sources (Kremer et al.
a,b). Nevertheless, the manual chlorine dispenser
still requires users to add chlorine during each water collec-
tion event, and to calculate the number of turns necessary
for their vessel size (International Centre for Diarrhoeal Dis-
ease Research, Bangladesh icddr,b ).
The Zimba automated batch chlorinator was invented to
reduce barriers to water treatment by focusing on automated
treatment at the community level. The Zimba attaches to
handpumps and dispenses a dose of 3 mL of NaOCl sol-
ution into a mixing chamber for every 10 L-batch of water
that ﬂows through the device. After chlorination, water is
ﬂushed by an automatic siphon into a storage reservoir
and dispensed via a tap (Figure 1). The Zimba does not
Figure 1 |Zimba automated chlorine dispenser. Figure provided by inventor Suprio Das. Figure showing(a) Outer box: upper part of outer box holds dosing chamber and lower part acts as
a secondary tank which water ﬂushes into after chlorination. (b) Dosing chamber: this chamber holds an automatic siphon and the chlorine dispenser. As untreated water from
the handpump starts ﬁlling up this chamber, 3 mL of sodium hypochlorite solution is ejected from the chlorine dispenser into this water. When the water level reaches the high
water level (10 L) the automatic siphon is triggered and this 10 L of treated water is ﬂushed into the secondary tank. (c) Siphon: water from the dosing chamber ﬂushes into the
secondary tank through the siphon. (d) Chlorine dispenser: this consists of a chlorine reservoir and a combination of interconnected pipes and tubes. Dimensions of the Zimba
are 76 ×45 ×25; the outer casing, dosing chamber and the siphon are made of ﬁberglass and the dispensers are made of acrylic.
33 N. Amin et al. |Field trial of an automated batch chlorinator system Journal of Water, Sanitation and Hygiene for Development |06.1 |2016
require custom-sized water collection vessels or manual
addition of chlorine. We conducted a small-scale trial to
assess acceptability, accuracy, and consistency of chlorine
dosing by the Zimba, and to assess the microbial water qual-
ity of Zimba-chlorinated municipal water.
The study was conducted from February to April (before the
rainy season) in 2012 among compounds in low-income neigh-
borhoods in the Mirpur neighborhood of Dhaka. A low-income
urban compound in these communities consists of multiple
households that share common cooking areas, toilets, and
water collection points, typically all owned by a single landlord.
In our study area, water was extracted through a motorized
pump attached to network pipes that connect to a deep bore-
well maintained by the Dhaka Water Supply and Sewerage
Authority (DWASA). The borewell was also equipped with a
broken chlorine injector; the operator of DWASA did not
know when it would be repaired. Regular interruptions in the
pump’s electricity supply cause the distribution system to
become unpressurized. DWASA also intentionally distributes
water intermittently in some areas because demand exceeds
supply. When the system becomes unpressurized, sewage can
be sucked into damaged pipes that pass through the open drai-
nage system (Kumpel & Nelson ).
Each of the water collection points (handpumps) in our
study area was located within a compound and was used for
drinking and other household uses. All study compounds
met the following eligibility criteria: (1) the water point
was located in a compound and shared by 5–30 households,
(2) the water point delivered water from the DWASA distri-
bution system, (3) the water was extracted by a manual
handpump, and (4) the water point was the compound’s pri-
mary drinking water source.
We selected Dhamalcot slum at Bhashantek, Mirpur, where
the household compounds were divided by four separate
streets. From these streets we purposively selected the two
longest streets and randomly assigned one street to control
and another street to treatment with the Zimba. We assigned
treatment by street to avoid contamination between treatment
and control groups. Fieldworkers used convenience sampling
to enroll six eligible compounds from the street of treatment
compounds and ﬁve eligible compounds from the street of
control compounds. Fieldworkers also used convenience
sampling to select ﬁve households from each treatment and
control compound to participate in household surveys at base-
line and end-line; mothers with at least one child under 5
years were given preference for enrollment (Figure S1).
Trained ﬁeldworkers visited eligible households to
describe the study prior to collecting baseline information.
Fieldworkers introduced the Zimba to mothers in the com-
pounds, explained its advantages and disadvantages, and
showed how it worked using pictorial cue cards. The ﬁeld-
worker provided a consent form written in Bengali and
requested mothers to discuss the study and the device with
other household members, then collected the signed con-
sent on the following visit. Fieldworkers also obtained
written consent from the landlord/compound managers.
The study protocol was reviewed and approved by the Insti-
tutional Scientiﬁc and Ethical Review Committees at the
International Centre for Diarrhoeal Disease Research, Ban-
gladesh (icddr,b) (protocol number # PR-09048).
Baseline survey and household water testing
Fieldworkers conducted quantitative surveys with mothers
(ﬁve surveys from each compound) to gather information
on demographic characteristics of households, perceptions
of drinking water quality, water collection and storage prac-
tice, water treatment practice and satisfaction with the
current water supply. In each compound, a ﬁeldworker then
tested the existing water supply (handpump and stored
water) from all households for water turbidity and free and
total chlorine using a digital colorimeter (LaMotte Model
1200, LaMotte Company, Chestertown, Maryland) and tur-
bidity meter (LaMotte Model 2020i, LaMotte Company,
Chestertown, Maryland). The ﬁeldworker then collected
handpump and stored water samples from all households
using 300 mL sterile sample collection bags containing a
sodium thiosulphate tablet (Nasco Whirl-Pak
Fort Atkinson, Wisconsin) to neutralize any chlorine that
34 N. Amin et al. |Field trial of an automated batch chlorinator system Journal of Water, Sanitation and Hygiene for Development |06.1 |2016
could be present. Samples were immediately placed into a
cold box, maintained at <10 WC with ice packs, and sent to
the Environmental Microbiology Laboratory at icddr,b to
assess levels of E. coli and total coliform contamination.
Description of the Zimba
The Zimba is made of three parts: a dispenser containing
diluted household bleach (NaOCl), a dosing chamber contain-
ing an automated siphon, and an outer box that holds the
siphon tank and the dispenser (Figure 1). The handmade
Zimba prototype cost about 100 US$ to produce, including
labor costs; it works without electricity and has no moving
parts. The Zimba’s chlorine dispenser can treat approximately
8,000 L of water (∼1 mg/L concentration of free chlorine in
source water) between each chlorine reﬁll. See supplemental
information for additional details (available in the online ver-
sion of this paper). The Zimba is mounted on an iron stand
approximately 30 cm in height. A chlorine dispenser compris-
ing a chlorine reservoir connected by tubes to two chambers
(pressure chamber and constant level chamber) sits on the
dosing tank. When untreated water from the handpump falls
by gravity into the dosing tank, positive air pressure pushes
the chlorine out from the trap through the ejection tube,
where it mixes with water in the dosing chamber. After this,
the water level in the dosing chamber rises until it reaches a
water level of 10 L. Then, the treated water ﬂows through
the siphon to the secondary storage tank. When the water
level goes down in the dosing chamber, the resulting negative
pressure pulls chlorine up from the constant level chamber to
ﬁll the trap. The trap was designed to hold 3 mL of NaOCl.
Chlorine purchase and dilution
Two ﬁeldworkers purchased household bleach (∼5.25%
NaOCl) from the local market and diluted it with distilled
water to a concentration of 0.6% NaOCl to achieve 2 mg/L
of free residual chlorine when added by the Zimba to source
water. The concentration of chlorine was closely monitored
before delivery. We eventually reduced the NaOCl concen-
tration to 0.4% to achieve ∼1.5 mg/L of free chlorine in
source water because study participants complained about
the strong smell of chlorine. The same two ﬁeldworkers
reﬁlled all Zimba dispensers with chlorine twice a week.
At least one day prior to installation of the Zimba, an interven-
tion promoter held compound-wide meetings with study
participants to introduce chlorinated water and its potential
health beneﬁts and to give instructions for using the Zimba.
During promotional activities, ﬁeldworkers advised study par-
ticipants to drink the treated water 30 minutes after collection
to allow time for disinfection. The ﬁeldworkers also requested
that study participants share this information with other
household members. With the help of a local handpump
mechanic, ﬁeldworkers increased the height of the handpump
by 12 inches and installed Zimba chlorine dispensers in the
six treatment compounds. The mechanic also maintained
the handpumps throughout the study period.
Follow-up and end-line surveys
During twice-weekly follow-up visits and one end-line visit,
ﬁeldworkers collected two types of water samples from
treatment households: treated Zimba water directly from
its secondary tank, and household stored drinking water.
From control households they collected handpump water
and stored drinking water. At the end of the three-month
intervention, ﬁeldworkers conducted an end-line quantitat-
ive survey to assess satisfaction with the current water
system and perceptions of water taste, smell, and water qual-
ity among control and treatment compounds enrolled at
baseline. Fieldworkers also administered the survey to new
households with children under 5 years old that moved
into the compounds during the study period.
Qualitative in-depth interviews
Fieldworkers used convenience sampling to select two
mothers with at least one child <5 years old from each treat-
ment compound. A trained ﬁeldworker used a written guide
to conduct in-depth interviews focusing on how the Zimba
chlorinator performed, how regularly they drank chlorinated
water treated by the Zimba, perceptions (likes/dislikes and
advantages/disadvantages) of chlorinated water and the
Zimba device, and changes in taste and smell of treated
water over the study period. Fieldworkers collected sugges-
tions for making the Zimba more user-friendly.
35 N. Amin et al. |Field trial of an automated batch chlorinator system Journal of Water, Sanitation and Hygiene for Development |06.1 |2016
Fieldworkers elicited perceptions among other family mem-
bers, relatives, and neighbors regarding the Zimba. In-depth
interviews were recorded using a digital audio recorder.
Microbial water quality testing
All water samples were ﬁltered within 6 hours of collection.
E. coli and total coliform concentrations were enumerated
using membrane ﬁltration following the United States
Environmental Protection Agency (USEPA) Standard
Method 1604 (USEPA ). In brief, 100 mL of each
sample was ﬁltered through a 0.45 micrometre ﬁlter, then
the ﬁlter was placed on MI agar media and incubated at
35 WC for 24 hours. Blue-colored colonies were enumerated
as E. coli and colonies that ﬂuoresced under long-wave
UV light (366 nm) were enumerated as total coliforms
(E. coli were included in the total coliform count). Agar
plates with 500 colony-forming units (CFU) were designated
as too numerous to count (TNTC) which follows previous
published protocols (Pickering et al. ;Peletz et al. ).
One duplicate sample was analyzed for every 10th sample col-
lected; one lab blank (100 mL distilled water) was ﬁltered
each day as a control. Plates with >500 CFU were not feasible
to count because the colonies cannot be distinguished from
each other; growth is also inhibited due to crowding.
Quantitative data analysis
To compare the mean difference between groups, microbial
water quality samples under the detection limit were assigned
the value of 0.5 CFU/100 mL and samples above the detec-
tion limit were assigned the value of 500 CFU/100 mL. To
compare the mean difference within groups and between con-
trol and treatment stored water samples we converted
bacterial counts into log
scale and performed regression
modeling, adjusted for clustering at the compound level. We
adjusted compound level clustering using robust standard
error of the mean difference. See supplemental information
for further details.
Qualitative data analysis
The ﬁeldworker who recorded all in-depth interviews down-
loaded them and transcribed them in Bengali so thematic
content analysis could be performed. The investigator,
N.A., manually coded the transcripts according to our
research objectives. After coding, he categorized the data
under different themes and matched these themes to factors
inﬂuencing acceptability and feasibility.
Two compounds (comprising 10 households each) in the
treatment group withdrew from the study after installation
of the Zimba and were not included in the analysis. One
withdrew because the additional time required to pump
the water into the siphon tank was inconvenient and the
other because the amount of space that the device occupied
interfered with cleaning utensils and washing clothes. Three
households in treatment compounds moved out during the
study period and were not included in the analysis. A total
of 24 (96%) control households (one household decided
not to participate following enrollment) and 30 (100%) treat-
ment households were interviewed at baseline. During the
end-line survey, ﬁeldworkers conducted interviews with 24
(96%) control and 17 (57%) treatment households. Mothers
from 12 treatment households (2 per compound) partici-
pated in qualitative data collection.
Baseline characteristics of control and treatment
Demographic and socioeconomic
At baseline, the age, education of respondents, number of
<5 years old children and other members per household,
and monthly income were comparable across control and
treatment households (Table S1).
Water collection and storage practice
Fourteen (58%) mothers in control households and 13 (43%)
mothers in treatment households collected their drinking
water using a plastic pitcher/jug (2–3 L). All control and treat-
ment households (100%) stored their drinking water; 19
(79%) control households and 20 (67%) treatment house-
holds reported usually covering their stored water with a lid.
36 N. Amin et al. |Field trial of an automated batch chlorinator system Journal of Water, Sanitation and Hygiene for Development |06.1 |2016
On average, water was available at handpumps for more than
20 hours per day in all households (Table S1). About 8 L of
water per person was collected for cooking, storing and drink-
ing in a typical day in both control and treatment households.
Among all treatment and control households, only one treat-
ment household reported treating their drinking water by
boiling (Table S1).
Stored water quality
Stored water samples at baseline contained negligible amounts
of free and total chlorine (mean free chlorine ¼0.10 mg/L,
SD ¼0.06 in control compounds, and 0.08 mg/L, SD ¼0.05
in treatment compounds). Microbial quality of stored water
was similar in control (log-mean CFU of E. coli ¼0.8) and
treatment (log-mean CFU of E. coli ¼0.6) households. At base-
line, samples of stored water from two (7%) treatment
households and one (4%) controlhousehold had free chlorine
within the 0.2–2.0 mg/L range (Table S1).
Follow-up and end-line visits
Accuracy and consistency of chlorine dosing at treatment
All water samples collected immediately after chlorination
from the Zimba (100%) were within the 0.2–2 mg/L range
for free chlorine (mean ¼1.3 mg/L, SD ¼0.54) and total
chlorine (mean ¼1.4 mg/L, SD ¼0.58). Mean free and
total chlorine levels in household stored water samples
were signiﬁcantly higher in treatment households compared
to control households (mean difference of free chlorine ¼
0.33, P<0.001). In treatment households, 16 (20%) stored
water samples contained <0.2 mg/L of free chlorine
(Table 1). Average free chlorine in water samples collected
directly from the Zimba was 1.3 mg/L and in stored water
was 0.5 mg/L (Table 1,Figure 2).
Microbial water quality in control and treatment
All processed laboratory blanks were free from contami-
nation with E. coli. After installation of the Zimba, levels
of bacterial contamination in stored water samples were
lower in treatment households compared to control house-
holds (log-mean difference E. coli count between
treatment vs. control households ¼0.43 CFU/100 mL,
P¼0.002 of water; and log-mean difference total coliform
count between treatment vs. control households ¼0.61
CFU/100 mL of water, P¼0.029) (Table 1). In treatment
households, 72% of stored water samples had <1 CFU/
100 mL E. coli, compared to 51% in control households
(proportion difference ¼21%, P¼0.004) (Figure 3). In treat-
ment households, stored water samples with free chlorine
within the 0.2–2 mg/L range had less bacterial contami-
nation (log-mean E. coli ¼0.3CFU/ 100 mL) compared
to samples with chlorine level <0.2 mg/L (log-mean E. coli
¼0.5 CFU/100 mL; log-mean difference ¼0.52, P¼0.001).
Only 6% of E. coli samples were TNTC so this did not
meaningfully affect E. coli analysis, but it may have affected
the total coliform analysis.
Acceptability and perception of water supply in control
and treatment households
At end-line, 3 (12%) mothers from control households stated
that they were not satisﬁed with their water due to its poor
quality, and 5 (29%) mothers from treatment households
mentioned that they were not satisﬁed with their water
due to the bad smell (chlorine). In control and treatment
households 100% of mothers mentioned that the drinking
water from their current water source is safe to drink (Sup-
plemental information Table S2).
Acceptability of Zimba
At end-line, only one (4%) respondent from a control house-
hold and ﬁve (29%) respondents from treatment households
reported a bad (chlorine) smell in their drinking water.
Among the Zimba users who kept using the Zimba for 12
weeks, only half (53%) the mothers thought the device
was easy to use, but most (88%) were satisﬁed with it. Thir-
teen (76%) mothers were satisﬁed with the water taste, and
12 (71%) were satisﬁed with the smell. Fourteen (85%)
mothers believed that drinking Zimba chlorinated water
was healthier for their families.
37 N. Amin et al. |Field trial of an automated batch chlorinator system Journal of Water, Sanitation and Hygiene for Development |06.1 |2016
During the qualitative in-depth interviews (n¼12) in treat-
ment households, most of the mothers (9 out of 12)
mentioned that the machine puriﬁed the water by killing
germs. Some respondents also described the Zimba as a
water ﬁlter. All mentioned that the water had a medicinal
smell, but they became accustomed to it during the course
Figure 2 |Free chlorine level in control (n¼24) and treatment (n¼23) handpumps, and
in stored water at control (n¼83) and stored water at treatment (n¼96)
households over time during follow-up visits, in Mirpur, Dhaka, 2012.
Figure 3 |Percentage of household on y-axis (control n¼83 and treatment n¼96) with 0
E. coli per 100 mL in stored water over time during follow-up visits, in Mirpur,
Table 1 |Water chlorine residual, turbidity, and fecal indicator bacteria concentration among control and treatment households during bi-weekly follow-up household visits, Mirpur,
Control group n(%) Treatment group n(%)
Mean difference between control vs.
treatment households (P-value)
Source water at
water Stored water
<5 23 (100) 96 (100) 24 (100) 23 (100) 82 (100)
Mean (SD) 1 (0.52) 0.72 (0.47) 0.73 (0.39) 1 (0.33) 0.73 (0.34) 0.30 (0.006) 0.02 (0.724)
Free chlorine (mg/L)
<0.2 14 (61) 69 (72) 21 (88) 0 16 (20)
0.2–2 9 (39) 27 (28) 3 (12) 23 (100) 66 (80)
Mean (SD) 0.18 (0.17) 0.17 (0.12) 0.12 (0.08) 1.3 (0.54) 0.5 (0.5) 0.06 (0.054) 0.33 (0.001)
Total chlorine (mg/L)
<0.2 13 (57) 57 (59) 17 (71) 0 9 (11)
0.2–2 10 (43) 39 (41) 7 (29) 19 (83) 71 (87)
>2 0 0 0 4 (17) 2 (2)
Mean (SD) 0.22 (0.17) 0.2 (0.12) 0.16 (0.09) 1.4 (0.58) 0.55 (0.52) 0.06 (0.102) 0.35 (0.001)
Log-mean E. coli
CFU/100 ml (SD)
0.45 (1) 0.54 (1.1) 0.4 (1) 0.16 (0.4) 0.11 (0.84) 0.05 (0.773) 0.43 (0.002)
CFU/100 ml (SD)
1.3 (1) 1.6 (1.1) 1.2 (1) 0.5 (0.9) 1 (1.2) 0.09 (0.029) 0.61 (0.002)
38 N. Amin et al. |Field trial of an automated batch chlorinator system Journal of Water, Sanitation and Hygiene for Development |06.1 |2016
of the study. All mothers also mentioned that they obtained
all drinking water from the Zimba because it was safe for
their children. Most mothers (10 out of 12) mentioned that
the ﬁrst few weeks after installation of the Zimba they
noticed a strong smell of chlorine but only two respondents
complained of bad taste. All mothers also mentioned that
they considered drinking chlorinated water to be safer
than drinking untreated water and that treating water with
chlorine could prevent diseases. Most users (9 out of 12)
reported that they liked the Zimba but collecting small
amounts of water (i.e., one glass or one jug [2–3 L]) took
more time and created a long queue. One mother said,
‘Before installing the machine (Zimba) we did not need to
wait for water, but now we have to wait for water which
makes a long queue.’Some (3 out of 12) mentioned that
the increased height of the handpump made it difﬁcult to
pump water, particularly for children. Mothers also men-
tioned that they would not be able to reﬁll the Zimba
chlorine dispenser because of its complexity. They also
requested technical assistance for repair and reﬁlling of
the Zimba dispenser.
The concentration of free residual chlorine in water samples
collected directly from Zimba automated chlorine dispen-
sers was consistently observed to be within the World
Health Organization (WHO) recommended range (0.2–
2 mg/L). Over a 10-week period, the percentage of house-
holds with stored water with a safe level of free chlorine
was 80% in treatment households, while it remained low
(28%) in control households. Despite the apparent dosing
success of the Zimba, 20% of stored water samples from
treatment households did not contain the WHO-rec-
ommended chlorine level, and 28% were contaminated
(>1 CFU/100 mL) with E. coli. Possible explanations for
the absence of detectable free chlorine include collecting
water from other sources, undetected Zimba dosing incon-
sistencies, or consumption of free chlorine as a result of
water handling that leads to re-contamination (Quick et al.
One important contribution to the low adoption rates of
POU water treatment using NaOCl is the unpleasant taste
and/or smell in treated water (Clasen & Edmondson ;
Albert et al. ;Luoto et al. ). A study in southeast
Africa suggested that participants in Ethiopia did not taste
the chlorine residual at 1.0 mg/L (sodium hypochlorite),
noticed the presence of chlorine at 2.0 mg/L, and found
the taste objectionable at 3.0 mg/L. But in Zambia partici-
pants found the taste of chlorine to be too strong at
2.0 mg/L (Lantagne ). In our study, the average free
residual in stored water was low (0.5 mg/L, SD ¼0.5, range
¼0.07–1.8 mg/L), but 29% of Zimba users had not become
accustomed to the chlorine taste and smell after three
months of use. It is possible that the combination of chlorine
compounds with organic materials in the water affects taste
perceptions, which would vary by geographic location, high-
lighting the importance of adjusting the dose of NaOCl in
future studies according to participant preferences. A
higher dose of free chlorine could improve disinfection,
but it is unlikely that users in this study would have accepted
a dose higher than 1.0 mg/L.
The DWASA pump supplying the study area was
equipped with a broken chlorine injector. The spike of
chlorine in the stored water of control households during
the 3rd to 5th weeks of the study (Figure S2) may have
been due to the chlorine injector being activated by
DWASA. The chlorine level of Zimba treated water did
not go beyond the WHO recommended range of free chlor-
ine when the injector was on. These results suggest that even
though DWASA was attempting to chlorinate the municipal
water, it did not provide safe water consistently, as has been
found in municipal systems in India (Brick et al. ;
Kumpel & Nelson ).
The Zimba dispensers dose in 10 L batches, so if the sec-
ondary tank empties then users need to ﬁll the 10 L tank
even when only a small quantity of water is required. To
pump 10 L of water using a typical handpump in Dhaka
takes an average of 60 seconds (range ¼32–117 seconds,
n¼18) if pumped continuously (Yoshika Crider, unpub-
lished data). Since mothers already spend substantial time
collecting water and carrying out other household tasks
(Hanchett et al. ), they might be unwilling to spend
the additional time for pumping 10 L water when they
require only 2–3 L. Since the water sources were close to
the households, the users did not collect or store large
volumes. A smaller batch chlorination volume could make
39 N. Amin et al. |Field trial of an automated batch chlorinator system Journal of Water, Sanitation and Hygiene for Development |06.1 |2016
water collection from the Zimba more efﬁcient in this
Several design changes could improve the Zimba. The
Zimba dispenser occupies signiﬁcant space (45 ×25 cm)
when installed, thus installation may not always be possible
due to space limitations in urban slums. Future iterations of
the Zimba could be more compact. The Zimba required fre-
quent visits from trained ﬁeld staff to reﬁll the dispensers,
which is an issue for its sustainability. The reservoir capacity
could be increased so that the need for reﬁlling is less fre-
quent. In addition the Zimba used a low concentration
NaOCl solution (0.4%), which is non-standard and requires
dilution before ﬁlling the Zimba dispenser. Future models of
the Zimba could aim to use a higher concentration of
NaOCl to reduce the need for dilution (Lantagne et al. ).
Some limitations to this study should be acknowledged.
No other similar technologies were available at the time of
this study to compare the efﬁcacy of the device. Further
studies should aim to compare the effectiveness of the
Zimba with other chlorine water treatment options. Techni-
cal assistance with the technology for the ﬁrst few weeks
might have increased adoption rates. In addition, the study
population was drawn from a small geographic area in a
low-income community in Mirpur, Dhaka; thus, the accept-
ability and uptake results may not be generalizable to other
low-income urban communities.
The Zimba automated dispenser overcomes some of the
most important barriers to low-cost decentralized chlori-
nation of drinking water. First, it eliminates the extra step
of adding chlorine after water collection, which saves time
for other household work (Luby et al. ). Second, the
Zimba is attached/locked to the handpump and automati-
cally treats water without the active participation of users.
Since household members cannot choose whether to chlor-
inate, they may be more likely to adjust to the smell and taste
of the consistently chlorinated water. Third, users do not
need to consider the size of their water collection vessel
since the collected water is passively dosed with a safe
residual chlorine level before they collect it in their vessels.
Although the Zimba was able to successfully and consist-
ently chlorinate household stored drinking water, further
work must be done to take this technology or other similar
technologies to scale. Essential next steps include improving
the user experience (Ahuja et al. ) and developing an
appropriate business model for reﬁlling chlorine and main-
tenance of the device.
This research protocol was funded by the United States
Agency for International Development (USAID). icddr,b
acknowledges with gratitude the commitment of USAID to
its research efforts. icddr,b is also thankful to the
Governments of Australia, Bangladesh, Canada, Sweden
and the UK for providing core/unrestricted support. The
authors gratefully acknowledge Meghan Scott for
thoughtful guidance and review of the manuscript. Suprio
Das, the inventor of the Zimba, contributed Figure 1 in
this manuscript. We would also like to thank Suprio Das
and Laura Stupin for manufacturing and installing the
Zimba devices evaluated in this study. We also thank
Nazrin Akter, Wasim Ahmed and Arifur Rahman for their
ﬁeld activities. We are also grateful to the study
participants for their valuable time.
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41 N. Amin et al. |Field trial of an automated batch chlorinator system Journal of Water, Sanitation and Hygiene for Development |06.1 |2016