[[Image:SolarDistiller.jpg|thumb|right|350px|Gabriele Diamanti's "Eliodomestico" solar-powered eco-distiller. The small, vat-like still is made entirely from terracotta and zinc-plated metal sheets. It is designed to be produced (and eventually repaired) by local craftsmen.]]
Desalination is used to remove salts from brackish or saline surface water and groundwater in order to render it acceptable for human consumption or other uses. Brackish water is defined as starting at having a Total Dissolved Solids content of 1,000 mg/l, and saline water as having 10,000 mg/l. It is increasingly employed to provide drinking-water because of a growing scarcity of fresh water driven by population growth, overexploitation of water resources and climate change. Desalination facilities exist all over the world, particularly in the eastern Mediterranean region, with use increasing on all continents. Small-scale desalination is used to supply fresh water on ships and to provide additional fresh water in some hot and arid regions.
Desalination by distillation produces water without chemical salts. The method can be expensive because of the capital investment needed and because fuel/charcoal is used to heat the water. However, solar distillation is inexpensive. The volume of water produced is generally low.
Most present applications of desalination are for estuarine water, coastal water and seawater. Desalination may also be applied to brackish inland waters (both surface water and groundwater) and may be used on board vessels. Small-scale desalination units also exist for household and community use and present specific challenges to effective operation and maintenance.
'''Household solar stills''' <br>
Household solar stills have not been widely promoted, yet can provide 2.5 – 3 litres per m2 surface area per day. However there is
scope to increase yields – more efficient and expensive stills (Aqua Solaris) have been tried that can increase volume to 40 litres per m2 per day. Water temperatures must be high, while the condensing surface should be as cool as possible – for this reason stills are most efficient in the early evening when water is still warm but temperature of the glass is a lot lower, and stills continue to produce water during the night. Water extraction for solar stills takes place by gravity of condensate to a gutter which leads to a container or tank.
The Watercone is a massproduced innovation that can produce 1.5 litres maximum per cone per day, but tends to be expensive. Solar stills can be constructed using local materials which are cheaper. There are key points to get right:
