I have been doing a lot of experimentation lately with solar salt water stills. I'm 9 blocks from the Pacific Ocean in So Cal, and there are almost no natural fresh water sources here-abouts. I've tried a variety of setups and, by far, the best setup I've achieved is with a thin clear plastic bowl and lid available from the Smart and Final warehouse stores out here. You put the lid, really a big shallow bowl itself, upside down in full sun, sit a tray of some kind full of salt water in the lid, then sit the upside down bowl itself down on top of the whole thing snapping it onto the lid to get an airtight seal. The salt water evaporates and fresh water condenses onto the inside of the upside down bowl and runs down the steeply sloped sides collecting in the lid. Even running 4 of these stills during all the sunny hours (not as much as you might think considering that a part of everyday there's high fog obscuring the sun), I've been lucky to distill out about 8 ounces of fresh water. One thing that helped was to put a pile of black rags as kind of a wick in the salt water. This seemed to increase the surface area available for evaporation and helped improve the output somewhat. I would work further on refining this addition if I spend any more time on this project.