Jax -- check this site out.....   appears dogs can get giardia, but symptoms aren't as bad as in humans.  Personally I wouldn't worry about it, but then again, you mentioned your dog has a sensitive subject. 

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I've had my dog everywhere, and he has drank from the most god-awful water, no problems.  Maybe some diarrhea, but who knows what that's from. 

I worry more about my dog digging up human feces in the QP, as they don't have privies, and I also pick up his crap at BWCA campsites.  Good way to get dogs banned from the BWCA and QP! 

cheers,

prouboy