Reflecting Mirrors and Solar Evaporation
While this idea is quite basic, it might also be quite efficient. The link is to a basic diagram.
What has been left out of the diagram is an expansion chamber where the heated water would be in an area with about 26 inches of vacuum. This would allow water that is 122 degrees Fahrenheit or about 50 degrees Celsius to boil.
Reflecting mirrors are used on most deep space telescopes because of their ability to effectively focus light. And by having water flowing in a "stream" that has a black matte finish (absorbs heat, doesn't reflect light well)with a glass covering made from safety glass, the water would essentially be in an oven.
To cool the purified or treated water, a condenser using copper tubes could be used. This would help to preheat untreated water at the same time.
And with reflecting mirrors, they can be tilted towards the sun for maximum reflection. With current parabolic mirrors, copper pipes are heated which have to conduct heat and also have some refraction lessening the efficiency of the system.
Also, by having a glass covering to focus all of the light possible on the water while trapping as much heat as possible, there is virtually no refraction.
And if anyone has any thoughts or suggestions, please feel free to comment on this.