I know this may not be exactly the type of thing we are looking for, but I think it is good to know what types of technologies exist out there- obviously some require power etc, but most if not all could be powered solar/wind energies stored in batteries.
You may or may not know Dean Kamen, but he is an inventor of the Segway and other things. As for this water purification invention, it supposedly works and he has created it in order to help create drinking from toxic, polluted waters in developing and third world countries. According to him, it is supposed to be a low-cost and low-energy water purifier. Take a look at the links I posted.