Solar still an appropriate technology for potable water need of remote villages of desert state of India — Rajasthan

Rajasthan, the largest state of the India faces a grim scenario in relation to water availability resources. Rajasthan has two-third of its area as desert and it faces scanty rainfall, recurring droughts in 3–4 years in a cycle of 5 years. It would be seen from the present status of drinking water detailed out of 237 blocks in Rajasthan that only 49 are safe in terms of ground water while 101 are critical and semi critical and 86 are over exploited. It is a hard reality that state dependence on ground water is 91% for drinking water. About 21,190 villages/habitations suffer from the problem of excessive salinity, 23,297 villages/habitations suffer from excess fluoride problem and 20,659 villages/habitations suffer from excess nitrate problem. Based on the WHO guidelines for drinking-water quality about 56% of the water sources are un-potable. But on other hand Rajasthan is blessed with ample amount of solar radiation. The arid parts of Rajasthan receive average maximum solar radiation of about 7.5 kW h/m2 in the month of May and minimum of about 4.6 kW h/m2 in the month of Dec & Jan. Part of this energy may be utilized to meet out drinking water need of remote area dwellers of Rajasthan. Solar distillation and desalination unit is most appropriate for remote area dwellers because it is economical, easy to construct and maintain. Most parts of Rajasthan have enough solar radiation available which is the prime input for the system. A low cost high efficiency solar still with porous evaporating surface is fabricated for the purpose and cost analysis is done to calculate the cost of water in this paper [Bassam et al., Experimental study of a solar still with sponge cubes in the basin, Energy Conserv. Manage., 44 (9) (2003) 1411–1418; Bouchekima et al., Performance study of the capillary film solar distiller, Desalination, 116 (1999) 185–192; Bassam et al., Water film cooling over the glass cover of a solar still including evaporation effect, Energy, 22 (1) (1997) 43–48]. Water samples are collected from a remote village of state and analyzed to find the quality of drinking water. The working habits and medical history of the villagers is also investigated to work out cost analysis more realistically.

The study shows that over exploitation of water and scanty rainfall has deteriorated quality of drinking water of the selected village. The water stored in the underground tank is also contaminated with pathogenic microbes. Due to low population density in state it is difficult to manage supply of drinking water to most parts of the state. Solar still can be economically used to provide potable water to such remote area dwellers of the state. This will help to improve the health of dwellers apart from meeting the need of drinking water. The cost of distilled water comes out to be less than Rs. 2 per liter even in the very first year which gradually reduces to Zero as per analysis shown in Table 3. It is much economic in comparison to the bottled water available in the market which costs around Rs. 10 per L in Indian market. If the initial investment of solar still for people living below poverty line is provided by the government this section of population may get access to potable water at almost zero cost.