Chlorine test strips The most widely used disinfectant for drinking water, chlorine is also important for sanitizing swimming pools, cooling towers, other industrial equipment, and in the treatment of municipal wastewater. Its measurement and control are vital for both safety and economic reasons. Chlorine exists in water as "free" chlorine (hypochlorite) or "combined" chlorine (chloramines). No measuring, set-up, clean-up, or chemical handling are necessary.