Dear Readers,
As if we don't already have enough to worry about, now your water heater may be a source of Legionella bacteria...
Many people know "Legionnaires Disease" from an outbreak that occurred in the summer of 1976 at a hotel hosting a convention of the American Legion in Philadelphia. 34 people died in that incident after suffering chest paints, headaches, vomiting, diarrhea and shortness of breath. All who perished developed pneumonia.
In the Philadelphia incident, the culprit was originally thought to be contaminated water found in the hotel's cooling towers; later research indicated the bacterium was probably in the water supply system.
Although Legionella bacteria can be found virtually anywhere in the natural environment in, for instance, ponds, lakes and groundwater, it can also thrive in municipal, industrial and home water supply systems. From a human perspective, problems arise when the Legionnaire's-contaminated water is aerosolized by a showerhead, faucet or cooling tower. Once the water droplets are airborne they can be inhaled or aspirated. Estimates on how many people are infected annually with Legionella vary widely, from a low of 10,000 to as much as 100,000. The US Centers for Disease Control says that many cases or Legionnaire's disease are either misdiagnosed or not reported. The disease has a mortality rate estimate of between 5 and 30 per cent. Middle aged and elderly people, and those with weakened immunity systems, are most at risk of infection.
In any case, the Canadian Institute of Plumbing and Heating now requires tank-type storage water heaters to be set at a minimum of 140 degrees in order to reduce the number of Legionella and other bacteria in the water supply. The bacteria actually die when the temperature reaches 130 or so, but because storage tank-type water heaters "stratify," meaning colder water sits on the bottom while hot water rises to the top, the temperature had to be raised to accommodate that phenomenon.
Several states in the US have already upgraded their plumbing codes to incorporate this change. The rest of the country will follow at some point in the near future. Legionnaire's bacterial contamination is not considered a problem in "instantaneous," or "tankless," water heaters.
Setting a water heater's thermostat to 140 degrees runs contrary to the accepted wisdom of the last several decades. To encourage energy savings, homeowners were told to set their water heater's thermostats to approximately 120 degrees. Raising the thermostat to 140 will result in greater standby losses from the water heater's surrounding jacket, resulting in higher energy bills. In addition, water exiting a water heater set to that temperature is hot enough to cause severe burns.
For many years building codes have addressed the potential dangers of hot water scalding and thermal shock by requiring anti-scald protection on the hot water supply system. Some scald prevention devices include pressure reduction and in-line pressure balancing mechanisms, made to be used at the point of use. There are also mixing valves available that are installed at the water heater's outlet port, providing system-wide protection.
Newer homes are likely to have been equipped with this type of safety equipment. Older homes built before building code changed to require anti-scald protection, and which still have the original fixtures, are thus a potential source of burns if a water heater thermostat is turned up above 120 degrees. Mixing valves can be installed on any domestic water supply system; fixtures such as shower and bathtub controls, and faucets, can be upgraded to the type that has scald protection built in.
Zolton Cohen is a former ASHI-certified home inspector based in Kalamazoo. Write to Zolton Cohen, Around the House, P.O. Box 2007, Kalamazoo, MI 49003, or contact him through Michigan Live at www.mlive.com/forums/homeimprovement/.
