Unfortunately, Giardia can be passed through the intestinal tract of nearly every warm-blooded animal in the world. So, the chances of some animal or human pooping upstream in the water or near the water & washed into the water by rainfall is reasonably good.

As for your previous experiences, it has been said that it's better to be lucky than rich or good=looking! <img src="/images/graemlins/laugh.gif" alt="" />

Sue