Well, to be honest I'm contemplating both. The waterfall would be shallow pools with pebbles. The reservoir in the bottom I'm still playing with, but km thinking deeper. My gut feeling from everything I've read is that if there are enough climbing out places it shouldn't be a problem...

But for "soaking" we're talking under an inch or so....so they can stand on the floor an keep head above the water. Splash pools!! :-)