Microbial growth in domestic hot water systems

In domestic hot water systems, surprisingly high numbers of bacteria are often observed, even higher numbers than acceptable in cold drinking water. Aesthetic problems such as bad smell or discolourization of the hot water and technical problems such as bacterial biofilms in the heat transfers preventing the heating og the water have been observed in hot water systems with high numbers of bacteria but also allergic reactions such as itching and blushing skin after contact with the water has been suggested to be related to the high numbers of bacteria. A corporation project together with the Statens Byggeforskningsinstitut has been established, and in the project a hot water system in an apartment block is investigated in details. This includes the cold drinking water which is the source for hot water, the hot water tank and the distribution system. A sampling system have been developed to follow the microbial growth on the inner surface of the hot water tank and in the distribution system. This system is used for investigations of the distribution of the bacteria and the bacterial growth in the hot water system. Another purpose is to quantify the bacterial growth in relation to quality of th cold water and operation conditions of the system such as e.g. hydraulic retention time and electrolytical corrosion protection.