Recently I've run across some articles downplaying the chances of getting Giardia, some going so far as to claim that getting it from drinking water is a "myth." I did a bunch of research to find out how often people actually get Giardia. I could find two studies where people were tested for Giardia before and after an outdoor trip. In one, either 2 or 3 people out of 35 got Giardia. In the other, 6 out of 25 got it! So it's common. Good hygiene is probably at least as important for gastro-intestinal health, but Giardia can be a very big deal indeed, as many of us have unfortunately found out for ourselves.
Anyway, I posted a lot more information here because I want people to know that while treating water is optional, Giardia is no myth. Please check it out!