A solar still is a low-tech way of distilling

Distillation

Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

 water, powered by the heat of the sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 (more precisely, the heat & humidity of the soil, and relative cool of the plastic). Two basic types of solar stills are box and pit stills. In a solar still, impure water is contained outside the collector, where it is evaporated by sunlight shining through clear plastic. The pure water vapour (and any other included volatile solvent) condenses on the cool inside plastic surface and drips down off of the weighted low point, where it is collected and removed. The box type is more sophisticated.

Overview

Solar stills are used in cases where rain, piped, or well water is impractical, such as in remote homes or during power outages. In Florida

Florida

Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

 and other hurricane target areas that frequently lose power for a few days, solar distillation can provide an alternate source of clean water.

Solar stills are occasionally used on a longer term basis in developing world settings. However, depending on environmental conditions, they usually produce a relatively small amount of water, and even less where the source is saline or brackish. If the source is inadequate, a compromise method is to mix the distilled water with the brackish or saline water purified with other methods - this gives a more adequate quantity and re-introduces the other source contaminants, while still lowering the salinity, and improving the taste.
The Water Pyramid

Water Pyramid

A Water Pyramid or WaterPyramid is a village-scale solar still, designed to distill water using solar energy for remote communities without easy access to clean, fresh water...

 is a larger version, which uses an inflatable dome as the condensing surface and can be used in tropical, rural areas.

Knowing how to put together a solar still can prove to be a useful survival skill

Survival skills

Survival skills are techniques a person may use in a dangerous situation to save themselves or others...

 and could provide an important means of potable water in the event of a wilderness emergency. Nevertheless, under typical conditions makeshift solar stills rarely produce enough water for long-term survival, and the sweat expended in building one can easily exceed its daily output. Solar stills can extract water from moisture in the ground but to increase the amount of moisture available to a solar still, water (fresh or saline

Saline water

Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....

) can be added inside or along the edges of the still. Where no water sources are readily available, shredded vegetation , wet soil/sand, urine or covered feces, can be used inside the pit. If only the natural soil moisture is used, the pit must eventually be moved as the productivity drops. To prevent losing moisture by taking apart the still to retrieve collected water a length of plastic tubing can be used to sip water as it accumulates.

See also

• Solar water disinfection
  Solar water disinfection
  Solar water disinfection, also known as SODIS is a method of disinfecting water using only sunlight and plastic PET bottles. SODIS is a free and effective method for decentralized water treatment, usually applied at the household level and is recommended by the World Health Organization as a viable...
  
   - uses the sun's infrared energy and heat to disinfect water, but does not distill (evaporate and condense) the water.
• Watermaker
  Watermaker
  A watermaker is a device used to obtain potable water by reverse osmosis of seawater. In boating and yachting circles, desalinators are often referred to as "watermakers".-Varieties:Many different versions are frequently used by long-distance ocean cruisers...
  
   - A filter to obtain clean water from seawater; used in large vessels.
• Solar cooker
  Solar cooker
  A solar cooker, or solar oven, is a device which uses the energy of sunlight to heat food or drink to cook it or sterilize it. High-tech versions, for example electric ovens powered by solar cells, are possible, and have some advantages such as being able to work in diffuse light. However at...
  
   - A similar device used to cook food.
• Freshwater
  Freshwater
  Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
  
   - Desalinated, clean drinking water.
• Desalination
  Desalination
  Desalination, desalinization, or desalinisation refers to any of several processes that remove some amount of salt and other minerals from saline water...
  
  - The process that removes salt from seawater

External links

• Making a solar still