slow sand filters.

One way to clean water is through a slow sand filter. A slow sand filter uses sand as a medium to produce a biological medium/layer that traps and filters bacteria and viruses. They are pretty easy to build and only require a few parts and a little patients. A rookie could build one with basic tools and a good set of instructions.
   There are still many municipalities that use slow sand filters to treat water so if you have concerns about its reliability, you can put those to rest.
 For a decent home size unit you will need a 55 gallon drum, some PVC pipe some wood, sand, gravel in pea size and also 1/1/2 in size. I also like to use landscape fabric to keep layers separated.
 Here is a PDF I copied that explains it better than I most likely can.
 http://www.preppers.info/uploads/Water_-_Slow_Sand_Filters.pdf
note,, most of the items can even come from salvage! or found cheap!

http://en.howtopedia.org/wiki/How_to_Filter_Water_with_a_Sand_Filter

 http://www.slowsandfilter.org/illustrations.html

Sam at The Human Path has a working model they use at the school and also teaches classes on this subject. If you are interested and live in the area let me know and I am sure Sam will let you take a look at his and also let you know when he will run a class on it again.

http://thehumanpath.com/