With spring cleaning in full swing, you’re letting your inner neat freak come out and no surface in your home is safe. Top to bottom, kitchen to bathroom, you’re in the zone, and you’re not only putting away the winter boots and jackets, you’re giving every room a thorough scrub-down to wash away the months of winter stuffiness. All that microscopic bacteria in your home doesn’t stand a chance.

Still, you may have missed a spot – one you can’t wipe down with a disinfectant spray. The plumbing system in your home could be growing bacteria without your knowledge, and among the possible harmful bacteria you could be ingesting is legionella – best known for causing outbreaks of Legionnaires’ disease. 

Legionnaires’ disease, or legionella pneumonia, causes flu-like symptoms and can be beaten by a healthy immune system, but is known to be particularly trying, and sometimes fatal, for those who aren’t in peak physical health. 

The Centers for Disease Control and Prevention estimate between 8,000 and 18,000 cases of Legionnaires’ disease lead to hospitalization in the U.S. each year, but because it’s easy to misdiagnose as the flu, it’s considered largely underreported.

Given the right conditions, a temperature between 68 and 120 degrees Fahrenheit, and the right food source, a slimy biofilm buildup, legionella will grow and flow with the water, becoming airborne and inhaled as it comes out of a shower head, faucet or other kind of spout.

While larger outbreaks of Legionnaires’ disease are more well-known due to the number of cases at one time – in a hospital or hotel, for instance – legionella can grow anywhere. Organizations like the American Society of Heating, Refrigerating and Air Conditioning Engineers place standards on risk management for bacterial growth in a commercial building’s water system, but single-family residences aren't regulated.

“It will grow anywhere in the piping system where conditions are favorable for growth,” says Ron L. George, a certified plumbing designer and president and founder of Plumb-Tech Design & Consulting Services in Monroe, Michigan. “And the conditions that make it favorable for growth are the water temperature and the nutrients that are available in the piping system.”

Despite the great risk bacterial growth poses, George notes it is 100 percent preventable in any building – and you can ensure your family is safe using the water in your home. Follow these recommendations to be sure you’re aware of the risks and taking the right steps to protect your home’s water supply from legionella.

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Don’t leave it up to someone else. If the lead levels in the water in Flint, Michigan, have taught us anything, it’s that we need to be proactive about purifying the water coming into our homes and can't assume water provided from a treatment plant is always safe.

“The idea that your water is just flat-out OK to drink, you just can’t make that assumption anymore,” says Larry Wasson, a certified general inspector and owner of Affiliated Inspectors in Chevy Chase, Maryland.

Municipal water treatment, if done properly, will purify water with chemicals – often chlorine – which will help to kill off any existing bacteria.

But chlorine oxidizes over a fairly short period of time, and as the water travels from the treatment plant out to the residences it services, the chlorine content diminishes. With the time it takes for water to travel to the farthest reaches of its service, the purification chemicals in the water may be almost undetectable – and therefore ineffective in fighting bacteria – when they reach your home.

Federal water conservation bills passed beginning in the 1990s have slowed the speed of water, making travel time from a treatment plant to the end of the line longer. It went from as quickly as two days to as long as two weeks, in some cases, George says. 

“What it’s doing is slowing down the flow of water in our water mains … allowing the chlorine to dissipate to the point where it’s not even measurable when it gets to the end of the water lines,” George says.

While the water may have been safe leaving the plant, it’s traveled through miles and miles of piping, and when there isn’t enough chlorine to kill off bacteria, biofilm or buildup on the pipes, bacteria could flow into the water. If the treatments have dissipated too much, water in the service lines could become more vulnerable to picking up contaminants from pipe corrosion, interruptions like water main breaks and other incidents that could introduce toxins into the water.

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Turn the water heater up. The most effective way to kill legionella and keep it from coming back is to make the environment inside the pipes inhospitable for bacteria, and it’s not hard to do. George recommends turning your water heater up to 140 degrees, which should kill any living legionella within five minutes, and then keep it at that temperature to ensure any newly introduced legionella won’t survive.

“One hundred percent of the buildings would be safe if you stored your water at 140 [degrees],” George says.

In contrast, the U.S. Department of Energy recommends turning your water heater down to 120 degrees to save energy and prevent scalding, which is more likely to occur at higher temperatures. But by doing so, George points out, “You’re actually bringing the temperature down into the ideal growth range.”

To heat your water enough to kill legionella and avoid scalding at the point of contact, many appliance manufacturers make thermostatic mixing valves, which inject cold water into the heated water to allow you to keep the water heater at a higher temperature while keeping what comes out of a shower head or faucet 120 degrees or below.

A thermostatic mixing valve can also help conserve energy when it comes to your water heater's use, explains Chris Carrier, global marketing communications manager for Reliance Worldwide Corporation, a manufacturer of plumbing products, including thermostatic mixing valves. "It'll extend the amount of hot water, so you get more hot water out of the tank – so you can still keep the capacity, even when going to a [smaller tank]," he says.

The addition to your water heater hookup provides an extra safety net to ensure the water coming out of faucets in your home won't be dangerously hot, and as a result it may even be a necessity by law. "In certain new construction, it just depends on what states or province you're in, there could be a code that requires a thermostatic mixing valve to get installed after the water heater," Carrier says.

Another way to keep your water heater temperature up without a greater risk of burning is to adjust the rotational limit on your shower handle, and decrease the maximum temperature for the shower head itself. Many shower fixture manufacturers provide instructions for making the adjustment, as they vary between make and model.

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Don’t turn it down, even when you leave. A higher water temperature capable of killing off legionella bacteria only works consistently if it’s kept consistent. That means turning the water heater temperature down when you go on vacation, for example, is only going to allow the water to cool to ideal temperature for legionella growth and become stagnant, which creates even more optimal conditions for bacteria because there isn't regular use of faucets or toilets to replenish the storage tank with a more recently treated supply.

“If you turn your water heater down to the vacation setting, they might as well take ‘Vacation’ off and have ‘Legionella Growth’ there,” George says.

A long vacancy of any kind can be cause for a greater concern for bacterial growth in the plumbing throughout a home due to its lower water heater temperature. Wasson recalls the high volume of foreclosures during the housing market crisis beginning in 2007 allowed for bacteria to grow in the pipes, putting new buyers at risk as soon as they moved in.

“The water heaters were full of stagnant water, just chock-full of bacteria, and when people would take a shower they would breathe in bacteria,” Wasson says.

It’s possible bacteria has grown anywhere you’ve left an optimal environment, but that doesn’t mean you need to move or buy all new piping. A good first step is to turn the water heater up to 140 degrees or above, and George recommends flushing the pipes with that hot water – avoiding touching the water, of course.

“Anytime you buy a new home or move into an apartment or anything like that, turn all the faucets on and let them run for a while – probably a good five minutes or so,” George says. “Depending on how far you are from the [municipal] water source, but you want to let it run until you know there’s some sort of chlorine residual in there.”

Tags: real estate, housing, existing home sales, bacteria


Devon Thorsby is the Real Estate editor at U.S. News & World Report, where she writes consumer-focused articles about the homebuying and selling process, home improvement, tenant rights and the state of the housing market.

She has appeared in media interviews across the U.S. including National Public Radio, WTOP (Washington, D.C.) and KOH (Reno, Nevada) and various print publications, as well as having served on panels discussing real estate development, city planning policy and homebuilding.

Previously, she served as a researcher of commercial real estate transactions and information, and is currently a member of the National Association of Real Estate Editors. Thorsby studied Political Science at the University of Michigan, where she also served as a news reporter and editor for the student newspaper The Michigan Daily. Follow her on Twitter or write to her at dthorsby@usnews.com.