Iv'e experienced 'severe intestinal upset' twice. I drank from a glacier fed, fast moving stream in Alaska. Then we moved further upstream to discover a FILTHY and abandoned hunting camp.I was ill within 48 hours. Later I drank from a piped water source on a California ranch with identical consequences. The only way to eliminate crypto is boiling and/or mechanical filtration. chemical treatment is still usefull, especially if you must travel light. I treat my water, run it through the filter and if there is a local religous authority get it blessed.<br><br>