Chlorine is heavily used for disinfection and different applications treat at different levels. (1mg/l is comparable to 1ppm)
Drinking water is treated at around 0.1 – 0.5ppm (Utility companies can temporarily increase this if local works are going on)
Cooling water systems are treated around 0.5 – 1ppm
Swimming pools are treated up to 3ppm
The disinfection of water storage tanks and down services is around the 50+ppm mark