I'm a first-time Chi owner, and I noticed this about Pablo, too...not much of a drinker, slurp-slurp and he's done. Lakes, too...he'll go in wrist-deep if it's hot...the first time we took him to the lake and our AWS, Kali, started retrieving, he started after her and stopped, as if to say, "I will save you, Senora Kali! Uh, you're good? Okaaay, I'll just wait here, then..."
I'm not pushing the swimming issue with Pabs, since we don't boat at all. It took us two years to teach our Dobie, Dary, to swim; he had no body fat and no loft to his fur, so he'd sink like a rock and start flailing! We called him the German U-Boat LOL! With patience and not pushing him, he finally got the hang of it, which served him well later in life when he had ortho surgery...the swimming was great, low-impact PT for him.
If you're concerned about dehydration, I've had some success "forcing" drinking by putting a little no-salt-added chicken stock in their water (the stuff in the box is better than the stuff in the can). Of course, you can't leave it down all day, but as a quick fix it works well.