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Rajasthan is the largest state in India, occupying just over 10% of the total area of the country. The Aravali range of hills, an important physiographic feature of the region, divides the state into two; the western region, which includes the Thar desert, forms an arid zone with mostly sandy soils, covering around 175 000 km2 (~67,570 mi2). The groundwater at handpumps and borewells at many locations in western Rajasthan is saline, making it unsuitable for drinking, and at some locations it also contains high levels of fluorides, leading to skeletal fluorosis when such sources are used for drinking. Given the low annual rainfall of western Rajasthan, human development in rural locations has been driven by the need to use water with maximum efficiency.
Exposure to waterborne infectious diseases is a significant issue in rural India, where almost three-quarters of the population lack access to a reliable source of safe water and where diarrhea and similar diseases linked to the consumption of water contaminated with pathogenic microbes represents a continuous threat to the local people. This is especially so in arid areas such as western Rajasthan, where treated water is a scarce resource.
Traditional approaches to water use efficiency - rainwater harvesting systems
Since many villages have no direct access to a satisfactory supply of groundwater, various traditional systems have been developed to harvest and store the small amount of rainwater that falls during the single annual monsoon in July-September, which typically represents around 85% of the annual rainfall of 150-300 mm (~6-12 in). These traditional systems include:
nadis:
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most rural villages have their own pond, or nadi, constructed by the further hollowing out of a natural surface depression; the position and size of a nadi has often dictated the location and scale of a village. Most nadis retain water for several months of the year but many run dry before the next rainy season, especially in recent years when the region has experienced repeated severe droughts.
talabs:
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these are surface reservoirs, usually created either (i) by building an embankment around a nadi or (ii) by building a wall or bund on the lower part of a sloping site, to retain rainwater. In some communities, the words nadi and talab are interchangeable. The water in nadis/talabs is often quite turbid (typically up to 100 turbidity units or more) and/or colored (due to algal growth), and therefore is not usually the first choice as a source of drinking water for the local people, when an alternative source is available. For example, villages near to major roads often have a piped supply from an external source, but these are highly unreliable. As a result, such communities would benefit from having an effective means of treating the locally available water when the external water supply fails.
tankas:
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typically, these are underground cisterns, lined with lime mortar or cement. Village community tankas are used for collection of surface runoff and also for storage of water collected from ponds or elsewhere (stored pond water is thereby reduced in turbidity); household tankas are used for water storage at the family level, and in a few buildings they may be linked to rooftop rainwater harvesting systems. In times of drought, such as in 1998-2003, water may be brought in by road-going tanker, funded by government or relief agencies, and then stored in the village tankas. Water is drawn from the tanka by bucket ("balti") and rope and then transferred to metal pots or earthenware pitchers for transport and further storage.
baoris:
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also known as stepwells, these are unique to Rajasthan and Gujarat, combining the practical functions of water harvesting and storage - they are typically shallow rectangular wells, built at the center of a depression and designed to catch the rainfall from the surrounding area.. One side is a broad set of stone steps, giving direct access to the water. The stepwells also performed religious and social functions in traditional societies, and the most complex examples have been described as "temples of water," as a result of their ornate arched galleries and landings (Livingston 2003).
Microbiological quality of harvested/stored water
While traditional systems can provide a supply of water for rural villagers, its microbiological condition is often poor, since it will have been harvested and collected as surface runoff and then stored under conditions that will often cause further contamination. For example, it is common for people to step into the water within a baori or talab in order to fill their pitchers. When such surface water is collected, individual villagers may cover the mouth of their pitcher with a cloth, or may pour the water into a second cloth-covered pitcher to sieve out the zooplankton that are carriers of guinea worm (Dracunculus medinensis).
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.
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As these Photograph shows, women may
drink surface water directly from a talab, using cupped hands to drink the water through the mesh of their headscarf veil ("dupatta"). Brightly coloured dupattas and saris of pink, orange
and red are typical of this part of Rajasthan. Water collection vessels made of iron and brass are also visible, alongside a plastic jerry can.Figure2 shows the village tanka in Tulesar Purohitan.
A range of different types of metal vessels are visible, including iron pitchers in the forground, with stainless steel and brass pitchers in the background.
Figure 3 shows children carrying water using steel and brass pitchers - only the poorest families use earthernware pitchers for carrying water, as they are easily broken. In the villages used in this
field study, water is carried only a short distance (typically less than 500 meters [~1/3 mi]), whereas in the interior of Rajasthan it may be several kilometers or more to the nearest water supply.
Figure 4 Here, a villager stirs fine sand ("balu mitti") into a bucket of turbid surface water – on settling, the sand will remove some of the particulates, thereby reducing the turbidity.
(Pkunar)
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