Drinking
water in the arid zone of western Rajasthan |
1.
Introduction 2.
Traditional
approaches to water use efficiency - water harvesting systems 3.
Microbiological
quality of harvested/stored water 4.
Solar
disinfection as a point-of-use water treatment system 5.
Optimizing the
solar disinfection procedure prior to field trials 6.
Field study 8.
Conclusions 10.
References
|
Rajasthan
is the largest state in Exposure
to waterborne infectious diseases is a significant issue in rural Traditional approaches to water use
efficiency - rainwater harvesting systems
|
Microbiological quality of harvested/stored water
For
the same reason, if a woman should need to drink water directly from a nadi or talab, she will often
use her headscarf veil (known locally as a "dupatta")
or the edge of her sari to filter the water during drinking. However, apart
from such simple filtration procedures, water is usually drunk straight from
the source, without any treatment. This is partly due to a lack of awareness
of the risks of transmission of disease via the water supply, but is also due
to the absence of a suitable method of treatment. For example, fuelwood is scarce in the region, so very few people are
able to boil their water before drinking, and the inconsistent availability
of chlorine tablets (usually through the community health worker) for the
treatment of water stored in tankas means that
people cannot always rely on this approach. Similarly, while alum ("fitkari") can be used as a coagulant to treat highly
turbid water in village community tankas, it is
expensive and erratically available (often, only in cities and larger towns).
As a result, such untreated supplies represent a potential means of
transmission of waterborne infectious diseases, including dysentery, cholera
and gastroenteritis, which are not removed by the traditional filtration
procedures described above. In our routine testing of such waters using field
kits for H2S-producing bacteria, we have found that almost all of the surface
water and stored water supplies are grossly contaminated. Water
is usually stored on a daily basis in traditional earthenware pitchers
("matkas"), where evaporation from the
surface reduces the water temperature, making it more pleasant to drink in
the hot climate. Thus villagers will often select water based on such
behavioral patterns, for example from the coolest available source in summer,
rather than considering the potential for waterborne disease. However, there
is also a traditional belief that storage in pitchers made from either copper
or brass helps improve the quality of the water, thereby reducing stomach
upsets and aiding well-being. The microbiological basis for this has been
confirmed by recent studies demonstrating that fecal coliform
bacteria are inactivated by storage for 48 hours in a traditional copper and
brass vessels (Tandon, Chhibber
and Reed 2005). However, water is rarely stored for that long, being usually
collected and consumed daily. In recent years, villagers have moved away from
copper vessels, such as when they use plastic containers to transport water
to school or work. This behavioral change may be driven by the ready
availability of such plastic items; for example, discarded plastic mineral
water bottles used by tourists are obtainable in villages near to highways.
Additionally, plastic is lighter, less expensive than traditional metal
pitchers, and may be seen as more "modern" than brass and copper
vessels. In our studies in rural Rajasthan, we have found that while most of
the villagers are aware of the traditional belief in the effectiveness of
copper and brass pots, they do not make use of such metal pitchers for water
storage, though a few make use of brass pitchers for collecting and carrying
water to the household. Given
the limited amount of safe water for drinking and the recent problems with
drought conditions in western Rajasthan, we felt that it would be worthwhile
to see whether solar disinfection might be a useful means of providing rural
villagers with an alternative source of safe drinking water. The Wellcome Trust |
Solar
disinfection as a point-of-use water treatment system
The
use of sunlight is one of the oldest recorded methods of water purification
in At
its simplest ("batch-process" solar disinfection), the method
involves filling a transparent plastic or glass vessel with contaminated
water and then keeping this vessel in full-strength sunlight for several
hours, to inactivate pathogenic microbes. Using discarded plastic (PET)
drinks bottles in laboratory and field experiments, research has demonstrated
that solar radiation can inactivate a wide range of microbes, including fecal
indicator bacteria such as E. coli, waterborne pathogenic bacteria such as
those responsible for cholera and dysentery, and certain viruses and protozoal parasites. Continuous-flow solar water
treatment systems have also been developed and evaluated, though these are
more complex and sophisticated in design and operation (for a more detailed
review of solar water treatment, see Reed 2004). Solar disinfection is the result of
two processes:
It
is generally accepted that optical inactivation due to solar UV radiation is
the main component of solar disinfection. However, research has shown a
synergistic interaction between optical and thermal inactivation at
temperatures above 45°C (~113°F), where the combined optical and
thermal effects act to inactivate bacteria at a faster rate than would be
predicted from the effect of each factor in isolation (Reed 2004). Since
the optical inactivation process involves the sunlight-driven production of
reactive oxygen species, solar disinfection is strongly influenced by the
level of dissolved oxygen in the water, being optimum only under
oxygen-saturated conditions; however, this is relatively easily achieved by
leaving a small air gap during filling, and then shaking the bottle (Reed
1997). The
optical inactivation process is also sensitive to water turbidity, being most
effective with water of low-to-moderate turbidity (typically up to100
turbidity units). For water of higher turbidity, a three-stage process can be
used: 1. Clarification - by sedimentation, filtration or coagulation/flocculation (in
Rajasthan, the villagers sometimes add dried sand, known locally as "balu mitti," to reduce the
turbidity of water with a high
level of suspended solids before use).
|
Optimizing
the solar disinfection procedure prior to field trials
Laboratory
trials, have compared the effectiveness of bottles
with transmissive, reflective and absorptive rear
surfaces by adding a suspension of Escherichia coli to pre-sterilized
distilled water. Our results have shown that while the black-backed bottles
were the most effective in inactivating fecal indicator bacteria under
full-strength sunlight, a reflective backing was best under sub-optimal
sunlight conditions (cloudy skies) where the rate of solar disinfection was
slowest, showing around 25% enhancement in the rate of inactivation under low
sunlight conditions, compared to transmissive and
absorptive rear surfaces. As a result of these experiments, we decided to
evaluate the custom-made 1-liter bottles with stainless steel reflective
backings under field conditions in western Rajasthan, since it is important
to have the best rate of inactivation under sub-optimal light conditions. Field study
Field locations The
villages of Tulesar Purohitan ,Tulesar Charan and Bambore Boarli lying within
the rural interior of Jodhpur district approximately 30 km (~19 mi) east of
Jodhpur city, were selected as suitable field locations to evaluate the
household-level use of solar disinfection. Each village has a population of
around 1500 persons. Tulesar Puohitan
and Bambor are mainly composed of members of the Rajpurohit caste, a vegetarian community that maintains
links with other ruling and religious groups such as the Brahmins, while Tulesar Charnan mostly
comprises the Meghwal caste, a non-vegetarian
occupational group engaged in tanning/weaving and similar manual activities. While
each village has its own talab, both villages are
connected by a pipeline that can provide safe, non-saline water from a borewell around 45 km (~28 mi) away. However, this
pipeline also supplies 40 other villages along the route, and water is only
available intermittently, due to frequent failures in the electricity supply
and to lack of an adequate supply in the borewell.
Typically, water is pumped to each village once every 10 days or so. In Tulesar Purohitan, the piped
water is stored in a large village community tanka
from where it is collected by bucket and rope, whereas in Tulesar
Charnan the external supply is via a standpost and community tap on the edge of the village,
which is supplemented by government water tanker every few days during the
dry season. Regardless of the source, water is transported to the home in
metal vessels, and then stored in earthenware matkas
before drinking, especially in the summer months, when the surface water
temperatures can exceed 50°C (~122°F). The
lack of a consistent supply of safe groundwater means that both communities
would benefit from an effective treatment system for their local surface
water. The villagers of Tulesar Purohitan
maintain and utilize their talab to a greater
extent than the villagers of Tulesar Charnan, with appropriate religious rituals/observances
that give due regard to its traditional role as a source of water; thus,
cattle dung is regularly removed from the immediate vicinity of the talab, and anyone found urinating or defecating in the catchment area is charged 50 rupees (just over US $1) as
a penalty. In Tulesar Charnan,
the people prefer to use the external water supplies (public standpost or government tanker), and only use the talab water when these external supplies are unavailable.
In both villages, animals are allowed free access to the talab,
to drink and bathe, creating further contamination and increasing the
turbidity of the water. We
began our initial work in 2002, selecting families in each village for a
year-long baseline study prior to the introduction of solar disinfection as
part of a further year's follow-up study. However, the ongoing drought meant
that all local talabs and nadis
were dry, and the people were entirely reliant on additional supplies of
clean water brought in by government tanker. The drought eased only in 2004,
and a change in plan was required, due to the shortened timescale of the
project: 40 families in each village were randomly assigned either to the
treatment group, who were to use solar disinfection, or to the control group,
who were to continue with their previous practices (20 families per group,
with around 4 adults and 3 children per family). Each family in the treatment
group received 12-15 custom-made 1-liter solar disinfection bottles and
reflectors. Most
of the families live in "pakka" (good
quality) houses, soundly constructed with bricks and cement, with a tiled
roof and a terrace, whereas the remainder are in
"kachcha" (makeshift) houses, with clay
walls and grass or brushwood roofs. Irrespective of the type of dwelling, all
families had either a cemented terrace or a cleared area close to the
dwelling where solar disinfection bottles could be kept in full sunlight for
most of the day. In
all families, the women and children are responsible for collection and
storage of water. In contrast with some other areas of |
Monthly
surveys of the incidence of gastroenteritis/diarrhea were carried out,
alongside testing of the local water supplies (all talab
and tanka water was found to be highly contaminated
on every test occasion, whereas the piped water supply tested negative for
bacteria contamination). Despite the turbidity and color of the surface
waters, solar experimental studies carried out in the laboratory at Kochi
using E. coli added to pre-sterilized water samples showed that the
rate of solar inactivation of fecal indicator bacteria in such waters was
broadly equal to that of non-turbid distilled water to which the same strain
of E. coli had been added. The
families in the treatment group who were using solar disinfection to treat
their drinking water reported substantially fewer incidences of
gastroenteritis/diarrhea than the control group in both villages, with an
overall reduction of around 70% across all seasons. There was also a widely
held view among those in the treatment group that drinking solar treated
water led to a greater sense of overall well-being and an enhanced ability to
work, attend school, etc. In the later stages of the field trials, this view
also spread to members of the control group, who felt a sense of exclusion
since they had not been given the solar disinfection bottles. Implementation
of solar disinfection began in January 2004, which is the cool season in
Rajasthan. At such times, the ambient daytime temperature is typically
20-25°C (~68-77°F), and people prefer to drink warmer water; thus the
solar treated water could be consumed at the end of a day's sunshine, and was
consistent with the traditional preferences of the local people. As the
temperature increased towards the annual maximum of around 42-45°C
(~107.5-113°F) in May-June, the water had to be kept indoors overnight in
order to reduce its temperature; this reduced its appeal to some of the
families, who were intermittent in their use of the bottles. However, many of
the villagers in the treatment groups were still positive about the use of
the system, since they could appreciate that a
closed bottle also blocked the access of flies and other insects to the
treated water. Some families developed their own procedures to reduce the
temperature of the water prior to consumption, for example by keeping the
bottles overnight in a half-filled earthen matka.
Individuals who took the bottles to work or school often covered them with
cloth to prevent the water from overheating on the following day, while
others cooled them in shaded ditches. A
more significant drawback to the use of the solar water treatment bottles in
summer was reported for those using unfiltered water directly from the talab; in such cases the treatment process gave the water
a foul smell, presumably due to the decomposition of phytoplankton and other microflora. For those families who filtered their water
before solar disinfection, it proved necessary to carry out cloth filtration
three times before treatment, in order to reduce this problem. Around
half of the bottles were lost or damaged over the year-long implementation
period; however, laboratory tests also showed that while the remaining
containers were often badly scratched by sand and grit, they were still able
to provide effective disinfection, even after a year of regular use. Several
users commented that the 1-liter bottles supplied by the project were too small,
and should be replaced by larger containers (e.g. 2-liter or 5-liter
bottles). In addition, several villagers commented that because the
containers were given entirely free of charge, they were not held in such
high regard as they would have been if a small charge had been levied. Any
follow-up work should investigate the idea of charging a nominal fee for the
container and reflector, in order to increase its worth in the eyes of the
end-users. Similar conclusions have been reached for other small-scale water
treatment systems (UNDP-World Bank Water and Sanitation Program 1999). Children
were often found to be the most enthusiastic adopters of solar water
treatment, taking responsibility for laying out the bottles each day, and
then making use of the bottles at school. More recently, youth groups have
been formed in both of the villages, and these have considerable promise for
the continued implementation of solar water treatment. In hindsight, the use
of a male researcher based outside the village created a barrier to
communication with the women of each household, as face-to-face discussions
could only be held in the presence of a village elder. A better strategy
would be to work through a female worker sited within the village as part of
a larger health awareness program, though this was outside the scope and
funding of our project. |
Conclusions
Field trials in
rural Rajasthan showed a measurable reduction in the incidence of
gastroenteritis and diarrhea in a case-controlled trial over a 1-year period,
demonstrating that solar disinfection can enable such households to widen
their sources of treated drinking water. The historical
record of the use of sunlight for the traditional ceremonial purification of
drinking water should assist its wider acceptance as a practical approach to
water treatment in rural References
Acra, A., Y. Karahagopian and Z. Raffoul.
1980. Water disinfection by solar radiation. Lancet II:1257-1258. UNDP-World Bank
Water and Sanitation Program. 1999. Willing to pay but unwilling to charge.
South Asia Field Note. Patwardhan., A.
R.1990. Our water our life. Reed, R. H.
1997. Sunshine and fresh air: A practical approach to combat waterborne
disease. Waterlines 15:27-29. Tandon, P., S. Chhibber, and R. H. Reed. 2005. Inactivation of
Escherichia coli and coliform bacteria in
traditional brass and earthenware water storage vessels. Antonie
van Leeuwenhoek 88:35-48. (Back to top)
Webmaster
Build up by P. Kumar
|