Water heating by a domestic water heater. Two conflicting safety issues affect water heater temperature—the risk of scalding from excessively hot water greater than , and the risk of incubating bacteria colonies, particularly "Legionella", in water that is not hot enough to kill them. Both risks are potentially life-threatening and are balanced by setting the water heater's thermostat to . The European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease recommend that hot water should be stored at and distributed so that a temperature of at least and preferably is achieved within one minute at points of use. If there
Disease in Imperial Rome was not ideal for combating diseases. Their sewer system, praised for its longevity, had many flaws. As "Water History"’s Roger Hanson explains, street drainage and sewage flowed through the same pipes, which led to sewage openings on the streets. Also, since most sewer systems were privately owned, they were also privately maintained and in turn neglected. Instead, citizens would turn to their latrines; if they lived on anything but the ground floor they would even throw their excrement onto the street. This led to exposure of sewage to flies, dogs, and bacteria, all of which helped spread disease among Romans.