Think first about your potential use of chemical agents. If you have a good cooking vessel and fire, boiling is far more efficient. If your travelling fast or without fire then the tablets are a better strategy. I use Potable Aqua. In the smaller vial I can fit @ 40 of the 50 sold. Thats lots of clean water- assuming I ever use the things before time degrades another supply <img src="/images/graemlins/grin.gif" alt="" />