[tt] Science News: The Case For Very Hot Water

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The Case For Very Hot Water
http://www.sciencenews.org/view/generic/id/37933/title/The_Case_for_Very_Hot_Water

By Janet Raloff
Web edition : Thursday, October 23rd, 2008

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.


"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."
[http://apps1.eere.energy.gov/consumer/your_home/water_heating/index
.cfm/mytopic=13090] 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. Indeed, 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 he 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 shower head."

Shower head? 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.