In a recent post, the comments evolved to a discussion of the world's problem. One of them is safe drinking water, over 1 billion people do not have access to safe drinking water! Here is a video from TED describing how lifesaver drinking bottles can help to solve this problem. He estimated that with 20B UK pounds, all the world could have safe drinking water.
Other approaches: LifeStraw, rapid sand filter system, or clay pot water filters (step by step guide of making clay pot water filters, a process which the inventor has declined to patent!)