Safe water supply without disinfection in a large city case study: Berlin.

Berlin's water supplies originate exclusively from groundwater. For sustainable water management, river water is treated by flocculation and filtration and used either for artificial groundwater recharge (rivers Spree and Havel) or for bank filtration (Nordgraben and Lake Tegel). Drinking water chlorination was abandoned in Berlin (West) in 1978, and in Berlin (East) in 1992, following German unification. Chlorine consumption for the purpose of weekly performance checks in the chlorination plants of Berlin's 11 waterworks and occasional chlorination within the pipe system following pipe burst events amounts to 2500 kg per year. Based on the annual water demand of 250 million cubic metres, this is equivalent to 0.01 mg of chlorine per litre. Microbiological monitoring at the 11 waterworks and at 383 sampling points within the pipe system shows CFU at less than 10/1 ml-1 and coliforms and E. coli invariably at 0/100 ml-1. In view of the low AOX content, a multiplication of bacteria within the pipe system can be expected to occur not at all or only to a small extent. Resource protection measures, filter backwashing and pipe system maintenance in observance of the relevant technical rules will continue to ensure that the quality of Berlin's drinking water meets stringent hygiene requirements without chlorination.