Domestic hot-water systems are frequently implicated as the source of legionellosis (Legionnaires’ disease) outbreaks. Very small quantities of Legionella, the bacteria that causes the disease, is commonly found in the ground, in water, and even in tap water. Legionella is not likely to become a health risk unless it begins to multiply and colonize. If not properly designed or maintained, a domestic hot water system (as well as other open water systems) can facilitate such growth....