Your water heater can be the source of two common health hazards: the risk of scalding and the risk of disease from bacteria that thrive in hot water inside the heater. These can be conflicting risks because eliminating one potentially makes the other more likely unless additional safeguards are taken. The temperature on gas-fired and electric water heaters is set by a thermostat dial on the heater tank. Most thermostat dials incorporate a detent at the 120 degrees Fahrenheit mark. As the dial is rotated, it will stop at that point and require slightly additional force to move it above or below that temperature. Many homeowners choose to keep the temperature below 120 degrees to reduce scalding risk or to save energy. But raising the temperature above 120 degrees is recommended by many health experts to reduce the risk of exposure to bacteria, as long as cautionary measures to avoid scalding are implemented, as well.
The most hazardous bacteria found in water heaters is Legionella pneumophila, known to be the source of Legionnaires' disease, a potentially fatal lung infection often misdiagnosed as common pneumonia. Trace amounts of this bacteria are often present in municipal water supplies but do not thrive in the cold temperatures. Once inside a hot water heater, however, Legionella bacteria multiplies and is conveyed through the household plumbing, where it may be inhaled in the aerosol mist that accompanies showering, bathing or even washing dishes in a sink. Very young children and elderly people are particularly at risk.
Water heater tank temperatures in the neighborhood of 120 degrees create a supportive environment for the presence of Legionella and other bacteria. The temperature setting on a water heater thermostat actually only represents a maximum temperature when the tank is full and completely heated. Temperatures in the tank often fall below the indicated maximum as hot water is used and cold water circulates into the heater. It is at these lower temperature ranges of 95 degrees to 115 degrees Fahrenheit that Legionella bacteria multiply and become established inside a water heater. A study by the American Society of Sanitary Engineering showed that the bacteria cease to multiply when water temperature reaches 120 degrees. They are not destroyed at that temperature, however, and can survive to be conveyed to an outlet such as a shower head or faucet.
Scalding injuries from hot water are a risk to all ages. But they are most likely to affect children and the elderly who often cannot react fast enough to remove themselves from overly hot water. Sensitivity to exposure to hot water increases exponentially as water temperature rises. At 120 degrees, skin requires an average of three minutes exposure to sustain a first-degree burn. At 131 degrees, burns can occur in as little as five seconds.
The American Society of Sanitary Engineering recommends setting the temperature of home water heaters to 135 degrees to 140 degrees Fahrenheit, a range shown to destroy bacteria such as Legionella. At those temperatures, bacteria can neither thrive or survive to contaminate fixtures downstream from the heater. Adjusting a water heater to a higher temperature must always be accompanied by the installation of anti-scald devices in the home by a licensed plumber to prevent potential burn injuries, if such safeguards are not already present.
Anti-scald devices are available in three types: A temperature-actuated mixing valve is placed near the water heater’s hot water outlet and automatically mixes cold water into the hot water to reduce the temperature to 120 degrees. An automatic compensating mixing valve is located at the point of use — normally a shower or tub — to blend cold water and bring the water temperature to a safe level just before it emerges from the shower head or tub spout. A temperature-limiting device is generally used at sinks and lavatories and keeps temperatures to a predetermined setting indicated on a manual dial.
Original reporting: https://homeguides.sfgate.com/turning-water-heater-up-kill-bacteria-54596.html
