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5 Times You Shouldn’t Use Tap Water

Water that’s safe to drink can still make you sick if you use it for certain purposes

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Tap water in the United States is some of the best in the world, and it must meet strict federal standards to ensure it’s safe to drink, according to the Centers for Disease Control and Prevention (CDC).

However, while it’s generally safe for drinking, tap water is not sterile, and there are a few situations in which using water straight from the faucet could endanger your health, according to experts and a CDC report published in the journal Emerging Infectious Diseases.  

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5 uses where tap water can be risky

  1. Continuous positive airway pressure (CPAP) machines
  2. Nasal irrigation devices including neti pots, bulb syringes, squeeze bottles and battery-operated pulsed water devices
  3. Portable humidifiers
  4. Contact lens cleaning/rinsing
  5. Cleaning/rinsing an open wound

The risk is higher for older adults and those with weakened immune systems.

Using water straight from the tap for those activities is a bad idea whether you have municipal water or get your water from a well because you could introduce a harmful pathogen into your body, says Rachel Noble, a microbiologist and professor in the Institute of Marine Sciences at the University of North Carolina in Chapel Hill.

It’s best to use distilled water or boiled tap water for those purposes, the CDC says.

What makes tap water risky in those instances?

Most tap water naturally contains low levels of microorganisms such as bacteria and amoebae, says Shanna Miko, an epidemic intelligence service officer with the waterborne disease prevention branch of the CDC.

The water is safe to drink because those pathogens typically get killed by stomach acid, she says. But the pathogens can multiply if they’re inhaled or introduced to more vulnerable parts of your body such as your eyes or nasal passages, potentially causing serious or deadly infections.

“Those are dark, moist places that don’t have the benefit of stomach acid to help neutralize these bugs,” Miko says.

Pathogens found in tap water such as Pseudomonas, nontuberculous mycobacteria and Legionella account for a significant percentage of the 120,000 hospitalizations and 7,000 deaths due to waterborne diseases annually, according to the CDC.

For contact lens wearers, a dangerous amoeba called Acanthamoeba that lurks in tap water can cause a severe type of eye infection that is difficult to treat and can even lead to blindness, the CDC says. Saline solution made for contact lenses is best to use for rinsing.


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In addition, a small number of cases of brain-eating amoeba have been linked to nasal rinsing, neti pots or similar devices, according to the CDC.

Survey: Many Americans not aware of the risk

About a third of Americans don’t realize that tap water can contain bacteria or other living organisms, according to an August 2021 CDC survey conducted by Miko and her colleagues.

Perhaps more concerning, many of those surveyed reported using tap water in risky ways: About 1 in 4 said they filled humidifiers or CPAP machines with tap water, 13 percent reported using tap water for nasal rinsing, and 9 percent said they use tap water for rinsing contact lenses.

Adults age 55 and older were somewhat less likely to use tap water for those activities compared to younger people, the survey found. However, a significant percentage — 22 percent — still reported filling respiratory devices with tap water, potentially endangering their health.

How to make tap water safe for medical uses

Miko says you can either boil tap water to sterilize it or buy distilled water for those medical uses. She notes that not all bottled or filtered water is sterile. Look for “distilled” or “sterile” on the label, she says.

To sterilize tap water yourself, boil the water for at least one minute (three minutes at elevations above 6,500 feet) and then let it cool before you use it.

More advice on how to stay safe and prevent infections

  • Use boiled water quickly. When water sits in a container for a prolonged time, any bacteria that were already in the container will start to multiply, Noble says. “Even if it’s just a few bacteria, they can grow quickly and form a biofilm,” she says. The FDA recommends storing boiled water in a clean, sealed container and using it within 24 hours.
  • Always wash and dry your hands well. Whether you’re putting in contact lenses or filling a humidifier, if your hands aren’t clean, you could inadvertently contaminate the process, Noble says.
  • Clean your equipment properly and frequently. It’s important to follow the manufacturer’s cleaning instructions for your specific device, Miko says. For example, most CPAP manufacturers recommend using soapy water to clean the tube, mask and humidifier reservoir every day and fully disinfecting the device at least once a week.

“It’s just a simple extra step,” Miko says.

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