More than two-third of the earth’s surface is covered
with water. Most of the available water is either present
as seawater or icebergs in the Polar Regions. More than
97% of the earth’s water is salty; rest around 2.6% is
fresh water. Less than 1% fresh water is within human
reach. Even this small fraction is believed to be adequate
to support life and vegetation on earth. Nature itself
provides most of the required fresh water, through hydrological
cycle. A very large-scale process of solar
distillation naturally produces fresh water. The essential
features of this process are thus summarized as the
production of vapours above the surface of the liquids,
the transport of vapours by winds, the cooling of air–
vapour mixture, condensation and precipitation. This
natural process is copied on a small scale in basin type
solar stills.