Just few information.As a microbiologist, working for a tap water research lab, and i'm pretty sure the regulation for pool and recreation area are realy strict, more than wastewater regulation, specially for the microbial part.
Usually (in europe, but it's the same thing in US) you need to do some filtration step (like sand filtration) to remove suspended matters, and also some pathogens who are not killed by chlorine. UV lamp is more and more used, specially for elimination of some viruses who are not monitored by regular fecal indicators, that's look normal for a state of the art water treatement plant and control of the water Quality. Chlorine is important for controling biofilm formation inside plumbing.