The parasite we know and love. Share your horror stories. Don't be shy... I've had it so many times it hardly affects me anymore.
I got it drinking water in the backcountry at Bandlier Nat. Monument. I was drinking about a gal. per day for 4 or 5 days. Didn't really hit me till about a month later. The belly cramps were extreme, I felt better if I lay in a fetal position. I seem to remember it lasting about a day. I just rode it out. I'm pretty sure it was giardia or some such critter. I might have a cast iron stomach though.
Purp- You should definitely give it a try. It's a very novel experience. Horrible gut cramps, asshole runs like a faucet, and your burps smell worse than farts. Just go find a body of standing water, preferably with some beavers, and drink up. You won't forget it. Claymation- Thats a good one. You must have a very strong immune system. The symptoms often last for weeks, some can't get rid of it for months. The last time I had beaver fever was at a Wild Earth gathering in the Walbran Valley. Two good upstanding campers volunteered to fetch water for the whole camp- Drinking water from the spring up yonder hill, dish water from the notoriously contaminated lake nearby. Someone asked where the drinking water was at. "Oh, just take some out of any of the blue jugs with the 'X' on the side. Upstanding camper #2 gets a worried look. "Uh... I was using the Xs for dishwater..." Worried glances all around. By this time half the camp must have already been contaminated. Soon began the telltale sulfur smelling burps. Many people were sick for the entire gathering, some for quite a while after. Myself, I had one good shit and was done with it. I am a champion. I will never want for water again. I'll drink from anywhere.
Probably spent a total of at least a couple months in the backcountry of various places, drinking out of streams and lakes and I've never had it and nor do I want it but I usually use a hand pump type filter.
Lucky. Been in a lot of camps, and despite the best efforts of those who know better, sanitation sometimes falls to th wayside. All in all though, it's probably strengthened my immune system quite a bit. Pretty gross though, it comes from shit-particles. Just try to drink only from the fastest moving part of the stream, as close as possible to the source, and you should do fine. Don't eat any shit.
Got it once right after I moved to my place in Humboldt in the 80s. I had an outhouse that was nothing more than a box over a hole. I got sick, it started to pour down rain and I got to spend alot of miserable time sitting on the box of a shitter with a cheap poncho on shivering.