Actually, they put enough chlorine in the water to cause cancer. Approximately 9% of bladder cancer cases and 15% of rectal cancer cases in the United States can be linked to drinking chlorinated water. Google "trihalomethanes drinking water".
I sure wouldn’t drink water from an “open” reservoir without boiling it or filtering it through a good filter. That seems so dangerous to me. I don’t drink the water from our town’s closed hilltop tank. We put in a very expensive filter system for drinking water and ice making.