Hot Water Circulation Systems

When building a facility, consider a plumbing system that recirculates hot water continuously.

Tiefenbrunner's group (Tiefenbrunner, F., A.  Arnold, P. Dierich, and K, Emde. "Occurrence and Distribution of Legionella pneumophila in Water Systems of Central European Private Homes.

" In: Barbaree, J. M., R. F. Breiman, and A. P. DuFour, eds. Legionella: Current Status and Emerging Perspectives. Washington , D.C. : American Society for Microbiology, 1993; 235-238) found that homes with hot water recirculation systems were less susceptible to legionellae growth than were homes without them. 

The installer must extend the recirculation line to the point farthest from the water heater. You should also flush new plumbing with chlorine. Your plumbing contractor can put a chlorine tablet in every length of pipe before installation. These tablets are available from plumbing supply stores. 

This is also the best time to consider installing an ultraviolet (UV) treatment system, particularly if immunocompromised persons reside in the house. The unit should be installed on the incoming water line to treat all water used in the house (i.e., rather than treating only the kitchen faucet). An ultraviolet unit effectively kills legionellae in the water that flows through it.  

UV units are not effective for large building plumbing systems already contaminated with legionellae; by the time the legionellae-free water leaving the unit reaches distant points in the piping system, it will be recontaminated with legionellae growing in scale and biofilm. 

However, UV units may be appropriate for small systems, especially ones that are essentially free of scale and biofilm (e.g., a new house). As for water heaters, gas models have been shown less conducive to Legionella than electric ones.

Tankless water heaters may also be a good choice, but there is no data to prove it because Legionella studies of these units have not been undertaken.