I haven't gotten giardia (for most of us the symptoms wouldn't show up until after we get home, since the incubation period is around 10 days), but my dog Hysson has!

The first time he got it was only 2 days after an overnight trip but almost 4 weeks after the previous trip. I'd been letting him drink out of streams and lakes, since he prefers that to drinking water out of his bowl.

All I know is that he basically exploded from the rear while we were on the way home from Seattle a couple of months ago. I stopped as soon as I could (had to get off the freeway), let him finish the job for the moment, mopped up with a couple of old towels (which I always take along in the car) and stuck towels and bedding in a plastic garbage bag (which had trash from the backpacking trip). Of course my car windows stayed wide open the rest of the way, I held my nose as much as possible and I stopped about every 20 minutes to let him out for another round of liquid effusions. Once (finally) home, I spend several hours scrubbing and disinfecting his crate and the car interior as well as letting poor Hysson out every 20-30 minutes. I finally spent $80 to have the car detailed, just to be sure.

Normally 24 to 36 hours without food and then half-rations fed in very small amounts several times per day will take care of any of Hysson's problems with his sensitive Labrador digestive system. However, these liquid explosions kept coming back (fortunately, all outdoors) about once a week. I talked to my-daughter-the-veterinarian about it several times. After the third round she was quite sure it was giardia (because of the frequent recurrence) despite the disparity of the incubation period. She sent me Flagyl via overnight mail. That cured the digestive problems promptly, but it took several weeks for the poor dog (who was looking quite skeletal by that time!) to gain back the lost weight.

All Hysson's water is now being filtered--no more drinking out of streams and lakes during dayhikes and backpacks!

Some years ago, a friend got giardia (diagnosed from lab tests) specifically from a spring where the water was coming right out of the ground. That was the only time on the trip that he didn't treat his water, and the incubation period was just right. Even with the antibiotics it kept coming back for several months. We found out much later that the spring was in a long-time popular hunting area, so the ground water was probably polluted long before the USFS started installing vault toilets there.

Of course wildlife can carry giardia, too, which is why it was once known as "beaver fever."

I strongly agree with handwashing and treating water. My spoon is my only "dishes," but it gets first licked clean and then rinsed off and dried after use, and dipped in boiling water before its next use.