Chlorine in water is reduced ...

Chlorine in water is reduced by adding a reducing agent. either sulphur dioxide as a gas or sodium sulphite or bisulphite as a liquid reagent. in an emergency situation or to reduce chlorine in water that is to be flushed to a watercourse solid sulphide chemicals can also be used. Adding a higher level and then reducing it after a contact time is a common practice, usually about 0.3 mg/l is left as residual for distribution though this depends on the nature of the distribution system. Alternatively you can use activated carbon to reduce it but be careful as this and the aeration others have suggested would then expose the water to contamination again.