Editing Solar still (section)

=== Pit still ===
A collector is placed at the bottom of a pit. Branches are placed vertically in the pit. The branches are long enough to extend over the edge of the pit and form a funnel to direct the water into the collector. A lid is then built over this funnel, using more branches, leaves, grasses, etc. Water is collected each morning.

This method relies on the formation of [[dew]] or [[frost]] on the receptacle, funnel, and lid. Forming dew collects on and runs down the outside of the funnel and into the receptacle. This water would typically [[evaporate]] with the morning sun and thus vanish, but the lid traps the evaporating water and raises the [[humidity]] within the trap, reducing the amount of lost water. The shade produced by the lid also reduces the temperature within the trap, which further reduces the rate of water loss to evaporation.

A solar still can be constructed with two–four stones, plastic film or transparent [[glass]], a central weight to make the funnel and a container for the condensate.<ref>{{Cite web|title=Uncle John's Portable Solar Water Distiller ( for Survival )|url=https://www.instructables.com/Uncle-Johns-portable-solar-water-distiller-Fo/|website=Instructables}}</ref> Better materials improve efficiency. A single sheet of plastic can replace the branches and leaves. Greater efficiency arises because the plastic is waterproof, preventing water vapour from escaping. The sheet is attached to the ground on all sides with stones or earth. Weighting the centre of the sheet forms the funnel. Condensate runs down it into the receptacle. One study of pit distillation found that angling the lid at 30 degrees angle captured the most water. The optimal water depth was about {{convert|1|in|order=flip}}.<ref>{{cite journal|last1=Khalifa|first1=Abdul Jabbar N.|last2=Hamood|first2=Ahmad M.|date=November 2009|title=Performance correlations for basin type solar stills|journal=Desalination|volume=249|issue=1|pages=24–28|doi=10.1016/j.desal.2009.06.011|bibcode=2009Desal.249...24K }}</ref>