The Case for Very Hot Water

For years, conservation advocates have told consumers to turn down the thermostat on their hot-water heaters — largely to save energy, but also to avoid scalding showers and baths.  At least for some people, however, this green tactic could prove dangerous, new studies indicate.

BUGGED? Hot-water heaters, like the one going into this new home, can prove major breeding grounds for certain lung-damaging bacteria. lisafx / iStockphoto

“The number one cause of waterborne disease outbreaks in the United States,” says environmental engineer Marc Edwards, “is not contaminants leaving the water treatment plant (we do a good job of killing those). It’s the pathogens that grow in home water heaters.”

Last weekend, seven reporters attending the Society of Environmental Journalists annual meeting toured Edwards’ lab of at Virginia Tech, in Blacksburg — and were treated to some sobering information about water quality. Like that in water heaters.

On its website, the Department of Energy notes that, “Although some manufacturers set water heater thermostats at 140 ºF, most households usually only require them set at 120 ºF.” For each 10º drop in temperature, consumers can expect to see a three to five percent savings on energy use. Moreover, DOE points out, setting that thermostat to 120º could extend the heater’s lifetime by slowing the buildup of minerals and corrosion within it.

What DOE and other energy-conservation sites don’t point out is that 140 ºF will kill a number of potentially lethal waterborne organisms, like the ones responsible for Legionnaire’s disease and NTM, short for nontuberculous mycobacterial infections. In contrast, 120º provides a nurturing environment for such toxic microbes

Owing to lead-poisoning concerns, people should never drink hot tap water. That’s why the primary route to respiratory disease from these germs comes through inhalation of the steam associated with showering or hot tubs. Infections due to these home-grown germs are estimated to kill 3,000 to 12,000 Americans annually, Edwards says.

How come we haven’t heard about this? Mistaken for flu, many cases remain off the radar screen, he says. But check the web and you’ll find Edwards wasn’t exaggerating about a growing link between hot-water heaters and disease. A few months ago in the Journal of Water and Health, Joseph O. Falkinham III, also at Virginia Tech, and his colleagues reported on a shower link to NTM in a 41-year-old New York City physician.

When X-rays from a scan of her chest confirmed the tell-tale nodules for this disease (caused by a bug that’s close kin to those responsible for tuberculosis and leprosy), Falkinham arranged to sample the plumbing in her bathroom. Mycobacterium avium cells were found in all samples. What the microbiologist found: The DNA fingerprint of the bacteria responsible the woman’s lung disease “is the same as the mycobacterium in her hot water, cold water and her showerhead.”

Showerhead? Yep. Unscrew the shower head, he said, and you’ll find “a lot of sediment, crud and slimy stuff.” A biofilm comprising a host of different bugs — including Mycobacterium — develop in the shower head.

With financing from a public interest group representing families of people with NTM, his team is now investigating the plumbing of some 50 households around the country to see if the water lines of other patients with the disease similarly host mycobacteria. “We’re about half-way through the study,” Falkinham told me yesterday, “and the answer is yes.”

So turn up the heat on their hot water heaters and these bugs will die off? Nope.

As with TB germs, once environmental mycobacteria find a human host, they settle in forever. Drugs can keep their numbers down or essentially put the microbes “to sleep,” as Falkinham describes it. But take the drugs away or stress the host and the disease can awaken, leaving its victim with coughs, fever, night sweats and sometimes diarrhea. Untreated, the disease can even kill.

The same essentially also occurs in home plumbing. Once piping or water heaters become infected, residual populations of germs take up permanent residence — usually in biofilms. Later, when the flow of water through plumbing is high, such as during a long shower, bits of biofilm can break loose from surfaces, seeding the water with germs. Some cells will readhere to the inside of piping — or your showerhead. Others will just fly out the faucet.

Falkinham’s investigations indicate that trace quantities of mycobacteria taint most water mains around the country. We just boost their populations once they enter home plumbing. Which raises the inevitable question: If these bugs are ubiquitous, why aren’t we all sick?

We probably are all susceptible to infections if concentrations of the microbes get high enough. But studies in the United States and Europe have identified certain populations that appear especially vulnerable. These include people with HIV, individuals with cystic fibrosis, and especially slender senior citizens.

The question now: Will the risks from contaminated plumbing systems diminish if we raise water-heater temperatures back up into the 140 °F range. No test of that has yet been conducted, although Falkinham is itching to start one.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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