If you are where water outdoors is plentiful, you can use a microfilter and a UV pen to sterilize the water. REI and other vendors have a nice selection. In a pinch I've even filled up from a puddle (after running the water through an old t shirt and letting it settle for a while) with these filters with no ill effects. Great for camping and foreign travel too. http://www.rei.com/category/4500030