As far as I know, every day (weather permitting) at the posted opening time of the pool (check the signs), the lifeguards gather all the kids together, have them sit on the steps of the temple, and do some sort of chant to the "water gods" and then the waterfall down the temple steps is turned on.
I wouldn't plan my trip around it, but it's something cute if you and your kids happen to be there first thing in the morning. And chances are this is something "unofficial", so don't be disappointed if it doesn't happen.