Scarcity of water has become a great challenge since 1990 onwards due to climate change and expansion of population. Access to clean drinking water for poor is a serious problem as they do not have any other water purification system available. To address this problem, different types of solar stills for converting brackish, sea or any poor quality water into good quality drinking water were developed. The first among them is "Thoyam", which consist of a shallow basin painted black to hold water to be purified, a conical shaped glass or transparent plastic cover and a channel at its lower portion to collect the distilled water.
When sunlight falls over the still, most of it passes through the cover and gets absorbed by the black surface of the basin. The water in the basin gets heated and evaporates and condenses on the cover. This condensed water flows down the slope and passes out of the still via the channel. This still could yield 3–4 L/m2/day with a recovery of 60–70% potable water. Later, two other designs namely, Basin type – single effect solar stills and multiple effect solar still were developed, which could fetch 3–4 L/m2/day and 12 L/m2/day, respectively with a recovery of 60–70% potable water.
