Using UV radiation is known to be an effective way to sterilize water. Why? Because the radiation kills the DNA of any living organisms in the water, thus making them unable to reproduce in the human body- or anywhere else, for that matter. The micro-organisms aren't dead, but they can't make any more of themselves!! Hahaha
And if you think about it, what do many of the African nations have plenty of? Well, I'm in Ghana right now, and I would argue that it is SUNSHINE. Plenty of UV rays to go around!! So I searched a bit online to find someone who may already be using this technology in the developing world.
This is what I found: http://waterwars.pulitzergateway.org/?p=558
which explains a pilot project in Nairobi where water is left in bottles out in the sun for a number of hours so that it becomes safe to drink. However, there are a number of drawbacks: e.g. you can't use it on rainy days, you can only treat small amounts at once etc. So it's not perfect- but it's a start! And I think it is a really interesting one at that. An idea worth working to improve.