The water doesn’t just get poured into the pool and left there. New water has to be added just to counteract evaporation and splashing. It is at the least circulated and filtered, but a public system is also probably going to do more automatic treating. The water quality is also monitored.All so true. You don't think of any of that stuff as a kid growing up and going to the public pool, but now just thinking about it makes me cringe. It's not like hotel pools, public pools, or Disney parks ever circulate fresh water in or at least not often. I'm not an expert on public pool water circulation, but I'm guessing you're also swimming in pee from kids who were there last week, the week before, and the week before that. So gross if you think about it. The pool might be filled with more pee than water.