It's about eight inches deep, as you can see by my scientificy measurement. So it can hold about six inches' depth of water.
I was surprised by some of the instructions:
See that? No diving! No jumping! "Do not dive into this pool. Diving into shallow water can result in a broken neck, paralysis, or death."
I can understand the warnings about watching children and emptying the pool; toddlers can drown in very little water. And electrocution, yes, that can happen with the kinds of things people keep outside during a pool party or barbecue, like boom boxes. But diving?
Most of us have no temptation to become the next Professor Splash, the amazing fellow who can fall 36 feet into 12 inches of water. If you watch the video at the link you'll see he actually does a belly flop, not a dive, so he's landing flat on the surface of the water rather than piercing it. But don't try that either.
Here I should write about how idiots and their obliging lawyers are ruining the country by doing moronic things, getting hurt, and suing everything in sight, turning us into petrified wusses instead of grown men and women who know better than to pull a David Boudia into an eight-inch-deep pool. So we wind up with instructions on the handles of chef's knives that say DO NOT PUT IN EYEBALL. (Not yet, no, but give it time.)
Anyway, don't worry about Tralfaz. He is absolutely terrified of the pool and won't go near it, full or empty. Another ten bucks down the toilet. Dogs are the second craziest species I know.