Most people picture dirty drinking water when they think of waterborne illness. But in the U.S. today, the germs that make the most people sick often come from a swimming pool, a hot tub, or the pipes inside a building.
Which Waterborne Illnesses Make the Most People Sick
Swimmer's ear leads by a wide margin. Based on CDC estimates of waterborne disease, otitis externa causes 4,670,000 illnesses a year – about 3.5 times the 1,330,000 from norovirus, the runner-up (4,670,000 ÷ 1,330,000).
After the top two, the numbers drop off sharply. Giardiasis and cryptosporidiosis, both parasite infections, sit close together at 415,000 and 322,000 cases. Campylobacteriosis rounds out the top five at 171,000 – less than 4% of the swimmer's ear total.
The split between ear and gut stands out most. Four of the five most common waterborne diseases are stomach illnesses, yet together they add up to 2,238,000 cases. One ear infection linked to swimming causes more than twice that. Keep in mind these are modeled estimates – the true number of cases in any given year can be higher or lower.
What the Top Five Illnesses Do
Swimmer's ear is an infection of the outer ear canal. It usually starts when water stays trapped in the ear after swimming or bathing, giving germs a warm, damp place to grow. It causes pain, itching, and swelling, but it doesn't spread from person to person.
The other four are stomach and gut illnesses. Norovirus is a highly contagious virus that brings on sudden vomiting and diarrhea. Giardiasis and cryptosporidiosis come from tiny parasites that cause watery diarrhea, cramps, and nausea. Campylobacteriosis is a bacterial infection with similar symptoms, often with fever.
Water is only one way these germs spread – contaminated food and contact with sick people or animals also play a role. Cryptosporidium is especially hard to control in pools because it can survive the chlorine levels that kill most other germs.
The Deadliest Waterborne Diseases
Top 5 Waterborne Diseases by Estimated Deaths in U.S.
www.consumershield.comThe illnesses that sicken the most people are not the ones that kill the most. Nontuberculous mycobacterial, or NTM, infections lead CDC death estimates with 3,800 deaths a year. That is nearly four times the 995 deaths from Legionnaires' disease in second place, and more than the other four leading causes of death combined at 2,639.
Pseudomonas shows up twice. Its lung infection, pneumonia, causes 730 deaths, and its bloodstream infection, septicemia, causes 695 – only 35 apart. Counted together, Pseudomonas would reach 1,425 deaths and move past Legionnaires' disease into second place.
The rankings flip for swimmer's ear. It is first for illnesses but fifth for deaths at 219 – roughly 1 death for every 21,000 cases. None of the four stomach illnesses from the most common list makes the top five for deaths at all.
The deadliest germs share a pattern. NTM, Legionella, and Pseudomonas live in the slimy film, called biofilm, that forms inside pipes, showerheads, and hot tubs. People usually get sick by breathing in tiny droplets from mist or steam, not by drinking. Older adults, smokers, people with lung disease, and anyone with a weakened immune system face the highest risk.
How Waterborne Germs Reach You
A century ago, diseases like cholera and typhoid spread through drinking water and killed many Americans. Modern water treatment and sanitation made them rare in the U.S. Today's leading threats come from recreation and from germs that thrive in plumbing.
You can get sick by swallowing water, breathing in mist, or having water stay in your ears. Pools, hot tubs, and splash pads can spread stomach germs when someone swallows even a small amount of water. Lakes, rivers, and oceans are untreated, so they may carry germs from sewage, runoff, or animal waste.
Large buildings like hospitals, hotels, and apartment towers add another risk. Their long, complex pipe systems let water sit and lose disinfectant, which gives biofilm germs room to grow. Drinking water problems still happen too, such as after a water main break, a flood, or contamination of a private well.
How to Lower Your Risk
A few simple habits cut down on the most common exposures:
- Dry your ears with a towel after swimming and tilt your head to let water drain.
- Try not to swallow pool, lake, or river water, and stay out of the water if you have diarrhea.
- Run taps and showers that haven't been used for a while, such as after a trip, to flush out stagnant water.
- Clean showerheads and follow the maker's instructions for home hot tubs and humidifiers.
- Boil or filter water from streams and lakes before drinking it when hiking or camping.
How to Check Your Water
If your home gets water from a community water system, your utility publishes a yearly water quality report. You can look yours up through the EPA's Consumer Confidence Report page, which shows what the water was tested for and any violations.
Private wells work differently. The EPA's private well guidance explains that well owners are responsible for the safety of their own water, so regular testing is up to you. Your local health department can often point you to a certified lab.
When to See a Doctor
Most stomach bugs from water clear up on their own. It may be a good idea to see a doctor if diarrhea lasts more than a few days, you notice signs of dehydration, or ear pain gets worse. A cough, fever, and shortness of breath after hot tub or spa use can point to Legionnaires' disease and need prompt care. Mention any recent swimming, travel, or hot tub use so your doctor can test for the right germ.
Swimmer's ear and stomach bugs make the most people sick, while germs growing inside plumbing cause the most deaths. Knowing where each one comes from makes it easier to avoid the most common waterborne diseases and spot trouble early.
