[Ferrotoral]

Water is a poison when introduced in large doses OR when directly applied to animal cells (makes them explode).

Lesson is, try to keep the chlorine levels low enough so that it eliminates the main problem (organics in the water supply) and does not cause any problems. The biggest problem is not health, but customer satisfaction. Chlorine also tastes bad and smells worse in higher concentrations. You put too much in there, long before it becomes hazardous, your people will simply stop using it.

Kind of defeats the purpose.