Along this same theme, I have often wondered if there is any data whatsoever to support the idea that streams today in the Sierra are more likely to be contaminated than they were 30 or 40 years ago. Back then we always drank from the streams, and only treated water that was standing and looked funky. Never had a problem or heard of one I have read some articles stating recent measurements of Giardiasis, but no comparison of current and past measurements.