Just found this on the BBC's website... interesting product in developement for the overlanding folk:
A group of researchers in South Africa has developed a filter that can purify water straight from the bottle.
It sits inside a tube that can be fitted on top of a bottle and purifies water as it is poured on a cup.
According to him the filter will not only stop harmful bacteria from getting into the water, it will also kill them.
"We cover the tea bag material with nano-structured fibres, and instead of tea inside the tea bag, we incorporate activated carbon.