Art - I've used the Lifestraw quite a bit and have yet to suffer any ill affects. I know people that have used them in third world countries supposed drinking water out of mud puddles with no I'll effects. I'd not do that but have drank from the Smokys in TN, Elk Mtns in NCO and the Snowys in SWY with one. I still prefer filter and boil from water sources, especially those running through pastures/rangeland or beaver looking areas.
