AWWA ACE63049

The effects of possible nutrient limitation and disinfectants on Legionella pneumophila and Mycobacterium avium complex (MAC) regrowth in domestic water heaters are of high interest. When an initial disinfectant residual of at least 0.25 mg/L chlorine or 0.40 mg/L monochloramine is maintained, no detectable regrowth occurred in glass reactors without extensive sediment present at 37º C. In the nutrient concentration range typically encountered in domestic water supplies, high levels of microbes always grew on Legionella and frequently on Mycobacterium media. This points to inherent problems in maintaining microbial purity of water in domestic water heaters without disinfectant, and points to the importance of other important physical control factors such as temperature. However, many nutrients markedly increased growth of microbes, including the free ammonia that forms after chloramine (chlorine combined with free ammonia) decays. Use of chloramine disinfectant can sometimes worsen regrowth of microbes in situations where chlorine has completely decayed relative to the situation when free chlorine has completely decayed. Includes 18 references, table, figures.