A mixing valve installed at the water heater reduces domestic hot-water supply temperatures. The outlet temperature of the ASSE 1017 point-of-source mixing valve shown here is adjustable from 80°F to 120°F.
A mixing valve installed at the water heater reduces domestic hot-water supply temperatures. The outlet temperature of the ASSE 1017 point-of-source mixing valve shown here is adjustable from 80°F to 120°F.

A.Dave Yates, a plumbing contractor in York, Pa., responds: This initiative actually got its start in Canada, when the Canadian Institute of Plumbing and Heating (CIPH) began requiring 140°F minimum temperatures in storage-tank water heaters to suppress bacteria numbers. This measure is aimed in particular at Legionella pneumophila sero-group 1, the bad boys that cause legionellosis, or legionnaires' disease, a pneumonialike respiratory disease.

Estimates of the number of deaths from potable hot- water system bacterial infections range widely, but 10,000 per year is the middle ground. Roughly 25 percent of all potable water heaters have measurable levels of Legionella pneumophila SG1, which thrive in water temperatures between 95°F and 115°F.

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