DOMESTIC HOT-WATER SYSTEMS

BACKGROUND

Domestic hot-water systems are frequently linked to Legionnaires' outbreaks. The term "domestic" applies to all nonprocess water used for lavatories, showers, drinking fountains, etc., in commercial, residential, and industrial settings. Disease transmission from domestic hot water may be by inhalation or aspiration of Legionella-contaminated aerosolized water. Water heaters that are maintained below 60 degrees C (140 degrees F) and contain scale and sediment tend to harbor the bacteria and provide essential nutrients for commensally micro-organisms that foster growth of L. pneumophila. 

MAINTENANCE

To minimize the growth of Legionella in the system, domestic hot water should be stored at a minimum of 60 degrees C (140 degrees F) and delivered at a minimum of 50 degrees C (122 degrees F) to all outlets. The hot-water tank should be drained periodically to remove scale and sediment and cleaned with chlorine solution if possible. The tank should be thoroughly rinsed to remove excess chlorine before reuse.

Eliminate dead legs when possible, or install heat tracing to maintain 50 degrees C (122 degrees F) in the lines. Rubber or silicone gaskets provide nutrients for the bacteria, and removing them will help control growth of the organism. Frequent flushing of these lines should also reduce growth.

Domestic hot-water recirculation pumps should run continuously. They should be excluded from energy conservation measures.

CONTROL

Raising the water-heater temperature can control or eliminate Legionella growth. Pasteurize the hot water system by raising the water-heater temperature to a minimum of 70 degrees C (158 degrees F) for 24 hours and then flushing each outlet for 20 minutes. It is important to flush all taps with the hot water because stagnant areas can "re-seed" the system. Exercise caution to avoid serious burns from the high water temperatures used in Pasteurization.

* Use of product names is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.

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