Potable Water is a world wide problem. The developement of appropriate technology for it's production would have tremendous socio-economic impact. Water born disease is a leading cause of death in some third world countries.
I pay anwhere between 60 cents to 1.00 dollar a gallon for drinking water depending on the quality of the container. If I don't mind drinking the chemicals leached from the cheap plastic bottles it's 60 cents. If I want something a little safer it's a buck.
The manufacture of solar evaporation units for producing clean water could involve several simple circuits.
You should be able to make a fairly efficient solar evaporation unit out of window glass, a shallow stainless steel tank, and an electronically controlled valve to control water level in the evaporator.
The water can be collected from about any source, including air conditioning units, rain runoff, or other sources of low contamination.
The electronic circuit would be a solar powered water level control unit. There is a circuit in one of my radio shack books I think. Any way, use the water level sensor to activate the a plunger type relay (powered by small solar charged batteries) that pushes against a simple spring loaded flapper valve to open and close a pathway for the water from the storage tank to the evaporator. As the water evaporates and is collected by what ever clever method you use, the level of the tank will eventually fall below the sensor level activating the relay and refilling the evaporator.
I can not off the top of my head remember what the heat of vaporization is for H2O. Its somewhere around 120 Calories/gram I think. Any way, by looking at a solar insolation table for an area of about the same latitude you can determine how much collector area you need.
There is another very unique way of collecting potable water that would involve the use of a solar circuit used to drive a fluid circulation circuit; but it would only work in areas of high humidity.
Potable water is a world wide problem. Come up with an appropriate technolgy to produce it and you will enhance the life of millions.
Get the cost down to around a 100 dollars a unit and I will sell a couple thousand of them myself.
Gavilan