I realize this is an 18C area but not being a QP I started it here. Please move to where you think is right.
Anyway I would like to discuss what has and has not worked.
I will start off with water purification. I like the idea of a biosand filter. They are cheap, easy to make and work well. Also most times they can be made from local materials.
Down side is they do not filter out chemical containments.
There are two types, slow sand and rapid sand. The quick ones will not filter the ecili and friends very well but will filter out the dirt.
Slow sand relies on "good" microbs to kill the bad ones but it takes longer for the water to filter through the system.
Here is an animation on how a slow sand filter works.