Solar distillation is the use of solar energy to evaporate the water and collect its condensate within the same closed system. Unlike other forms of water purification, it can convert salty or brackish water into fresh drinking water (ie, desalination). The structure which houses the process is known as a volatile solar still and while the size, dimensions, materials and configuration are varied all rely on simple procedure in which a solution influent enters the system and the solvents left in the effluent leaving the salt solute behind.
Solar distillation differs from other forms of desalination that are more energy intensive, such as methods such as reverse osmosis, or simply boiling water due to its use of free energy. A very common example, and by far the greatest of solar distillation is the natural cycle of water that the Earth experiences.
The fundamental aspects of a site have still remained unchanged since antiquity, design simplicity is one of the main benefits of solar energy. However, there are many variations on the typical single slope / basin issue yet and these can fall into one of two categories, active or passive. These labels classify the still by the method it uses to acquire the energy to drive the evaporation of water. Passive solar cameras are, of course, more conventional and have been the only ones discussed up to this point. Active stills, however, can get "waste" heat from a myriad of sources. A good insulation is necessary to reduce thermal losses and prolong the evaporation process even at night. The insulation that can be used include things like polystyrene foam with a polypropylene cover, or wool (which can retain some of its insulation even when wet).