Had this gadget been a little less expensive, it could gain more impact in the third world countries where the main cause of deaths is contaminated water. For those who can afford, SteriPEN is a UV water purifier which purifies water with the help of Ultraviolet light. Just stir it in a glass of water for less than one minute and it effectively kills germs, bacteria and protozoa. It works on 4 AA batteries and weighs 227 grams.
It is available here for Â£149.00 (US$279). Another alternative here.