Summary: Open air-cooled steam distillation introduces enough variables that practical day-to-day distillation is not likely. Heat exchangers that make hot water as
a by-product look the most promising for primitive water distillation.
All of the above methods assume some sort of heat source that can produce steam. This assumption could be a problem for many areas due to the near constant rain and lack of firewood, coal, tar or other burnable resource. Some areas will be able to use hot earths crust to great advantage.
Warning: Hot Steam, hot water and hot metal will cause server burns as it transfers it heat to the skin of the body rapidly.
The amount of heat given off when steam changes back to water is 540 calorie/gram (called heat of vaporization). The amount of heat it takes to raise one gram of water one degree C is 1 calorie. Thus one can see a lot of heat is capable of being transferred to the skin for very little amount of steam.
Using these numbers it is easy to show that one can expect to produce hot waste water of about 7 (above 190 degree F) to 14 (above 140 degree F) times more volume of output water than the input water that was converted to steam in the first place. This assumes a room temperature of about 70 degree F as the starting temperature for the water.
Offered by Mike.