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
Coral disease has not been possible to identify the pathogens responsible for the disease and culture them in the laboratory; that the coral is sick and the tissue is necrotic is apparent, but whether the fungi or bacteria present caused the disease or merely fed on the already dying tissue is not clear. There is also a minute crab a millimetre or so wide which is often associated with diseased corals, but whether it introduces the disease or just moves in to consume the necrotic tissue is uncertain. Some of the bacteria found on diseased corals are terrestrial species that are not