This is a great project to purify any water to get drinking water. It uses no electricity or man made heat, just the power of the sun. These stills even work in winter.
This project from offthegridnews.com shows you how to build one and after reading the full article I would highly recommend reading the comments at the end of the page, they gave me more info on how to adapt and make this work even better.
Solar stills have been used for hundreds of years, obviously not like this still but using simple clear plastic and stones. This still will have you hydrated and feeling good about having a way to purify water in s SHTF situation.