I was just reading about SODIS, which I had never heard about before. Which is Solar water disinfection. Basically you put a bottle of water out in the sun and the UV rays of the sun will kill most of the stuff in the water. I am surprised I had not heard of it before, since it sounds so easy. Also here in the US, everyone has a ton of clear plastic bottles. From soda and water bottles. They are like every where. They are actually like a trash problem because they are every where in the world now. Where I live it is always hot and sunny too, so it is like amazingly easy to get a bottle and stick it in the sun, and boom clean water!
The flaws is that it doesn't get rid of chemicals. So it isn't going to replace filtering water, though it does solve the issue of having to boil water. Sticking a bottle in the sun is a lot easier than boiling it, and its a lot cheaper as well. The other flaw is that you need really clear water, and the bottle needs to be clear without a lot of damage, because the UV wont penetrate through dirty or cloudy water.
Also it doesn't sound like it kills everything, it just kills enough that you are unlikely to get sick. Still I found it a very interesting idea. It isn't perfect but damn cheap and easy.