Bio Sand Water Filter
BioSand Water Filters @www.friendlywaterfortheworld.com. This non profit out of Olympia, Wa provides inexpensive, durable biosand filters for approx $50 providing clean water to a family lasting for up to 30 years with almost no maintenance.
Rather than go into the hows, whys and what-for's, I will direct you to that area of the website so you can read what you want of it.
http://friendlywater.net/HOW This page will give you basic information on their product. You can also contact them by email at