In the April 2009 issue of Real Simple, it talks about PUR Packets. They're little powder packets that help clean water into drinking water for people all over the world. The little packets are $.10 each and it cleans enough drinking water for a child for 5 days. For a DOLLAR, you can give fresh water to a child for 50 days! That's pretty cool! No new wells need to be built, this just cleans the water.
Check it out at csdw.org (Think Children's Safe Drinking Water).