Recently in a forum I frequent, an energy auditor basically went on a tirade that we were essentially harming & possibly killing people by encouraging individuals to turn their water heaters down to 120°. The reason for this concern; old studies found online about Legionella possibly being spread via water heaters & showers. This was also exacerbated by some selective quoting from groups like OSHA who state (January 1999 Directive):
Domestic hot-water systems are frequently linked to Legionnaires’ outbreaks… To minimize the growth of Legionella in the system, domestic hot water should be stored at a minimum of 60°C (140°F) and delivered at a minimum of 50°C (122°F) to all outlets… Domestic hot-water recirculation pumps should run continuously. They should be excluded from energy conservation measures. (Of course it doesn’t help that “domestic” systems also include commercial & industrial facilities like hospitals which have had numerous outbreaks)
The Who, What, How & Why’s
Legionnaires’ disease (LEE-juh-nares) is a type of pneumonia caused by a type of naturally occurring bacteria called Legionella found usually in fresh water and the soil. For it to multiply it needs large areas of stagnant water between 69° – 122° (the optimal temperature range is 95° – 115°) and requires one to inhale it or swallow incorrectly, thus getting it into ones lungs. This disease & associated bacteria were discovered and named when a large group attending an American Legion convention in 1976 came down with it (221 infected – 34 died). (For More: CDC Patient Fact Sheet)
Cause for concern?
First off, while the CDC estimates that 8000 – 18000 are infected each year, the published numbers posted do not back them up. For example, Kentucky has averaged 5 cases per year, and even with (CT – 72, MA- 211, ME – 18) the numbers do not compute especially when they say that “we are now looking for this disease whenever a patient has pneumonia.” As they mention, older adults, smokers and people with weakened immune systems are particularly susceptible. (EDIT: to see actual stats of all reportable diseases including this one http://www.cdc.gov/mmwr/mmwr_wk.html – there have been a total of 3354 reported as of today for this year so the 8000 number is plausible if only 1 in 3 seeks medical attention)
Mayo Clinic: Although it’s possible to contract Legionnaires’ disease from home plumbing systems, most outbreaks have occurred in large buildings, perhaps because complex systems allow the bacteria to grow and spread more easily.
EPA (1999 Study): Legionella are considered opportunistic pathogens because, although they are highly prevalent in the environment, relatively few people develop a clinical infection. Yu and colleagues (1993) characterized the attack rate for Legionella as “strikingly low.” /// This case-control comparison showed a negative association between showering and acquiring Legionnaires ‘ disease, although earlier studies have sometimes reported a positive association with showering.
ASHRAE: Although aerosolization via showering is intuitively attractive, showering has not been shown to be a major disseminator of Legionella.
Personally with groups like the CDC, not even mentioning showers via there patient fact sheets and the information above, I don’t see a cause for concern for most households. I see more of an issue with children and others getting scalded from hot water heaters being set to high which (as I recall) was the original driver for lowering the temperatures on water heaters.
Common Sense & Misc. Tips:
- If you are in an at-risk group – talk to your doctor
- If you do reset your water heater and have anti-scald devices on your faucets, they probably need to be adjusted as they were set based on your original water heater temperature
- If you really needed a reason to drain your hot water tank – this is it (especially for electric ones as many attribute the build up at the bottom as a great breading area)
- Use distilled water in humidifiers, especially for the portable ones used when someone is sick
- If you have a bathroom that is hardly ever used & you are concerned about this (i.e. company is coming), drain the hot water heater, turn the vent on & let the water run for a while in said room to eliminate the stagnant water
- Make sure your whirlpool, spa, misters, and other items are properly maintained & disinfected per the manufacturer’s directions