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In 2020, a Centers for Disease Control and Prevention (CDC) study estimated that waterborne illnesses affect around around 7.2 million Americans annually. These illnesses can spread through drinking water, recreational bodies of water like swimming pools and lakes, and via water used for agriculture.

What is a waterborne illness?

Waterborne illnesses are diseases caused by pathogens — bacteria, viruses, and parasites — that travel via water and are contracted by drinking or encountering contaminated water.

What are the most common waterborne illnesses?

Per CDC estimates, the five most common waterborne illnesses in the US are:

  • Otitis externa or "swimmer’s ear": A bacterial infection that typically occurs when water stays in the outer ear canal for too long. Although more prevalent among children, anyone can get swimmer’s ear. It’s not contagious.
  • Norovirus: A highly contagious virus that spreads through contaminated food or water — it’s considered both a foodborne and waterborne illness. It often spreads when an infected person handles food without washing their hands first.
  • Giardiasis: A waterborne illness triggered by the microscopic parasite Giardia duodenalis. Giardia parasites spreads by being ingested in contaminated water or food. After infection, the parasite lives in the intestines and can be passed through fecal matter.
  • Cryptosporidiosis: Cryptosporidium, often called “Crypto,” is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. The primary symptom of a Cryptosporidium infection is watery diarrhea. Other symptoms include stomach cramps or pain, dehydration, nausea, vomiting, fever, and weight loss. It can be spread through drinking contaminated water or coming in contact with contaminated fecal matter.
  • Campylobacteriosis: An illness caused by the bacteria Campylobacter, and the most common bacterial cause of diarrheal illness in the United States. Campylobacter spreads mainly through consumption of raw or undercooked poultry, or foods that have been in contact with raw poultry. It can also be transmitted through other foods, contact with infected animals, and untreated water.
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Otitis externa, also known as swimmer’s ear, affects up to 7.3 million people (nearly the population of Arizona) every year, and Norovirus affects up to 5.5 million people (a bit fewer than live in Minnesota).

How many people die from waterborne illnesses every year?

The CDC estimates that 6,630 people die annually from waterborne illnesses. The waterborne illness estimated to cause the highest number of deaths is nontuberculous mycobacterial (NTM) infection, followed by Legionnaires’ disease, pseudomonas (pneumonia and septicemia), and otitis externa or swimmer’s ear.[1]

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Along with deaths, these illnesses are also estimated to lead to the most hospitalizations. NTM infections are estimated to cause the most fatalities and hospitalizations.

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What is recreational water illness?

Recreational water illnesses are spread by swallowing, inhaling or having contact with contaminated water in swimming pools, hot tubs, water parks, water play areas, interactive fountains, lakes, rivers, or oceans.

According to the CDC’s National Outbreak Reporting System, recreational water illnesses were responsible for 50% or more of reported waterborne illnesses from 1995 to 2021, except for 2017, 2019, and 2020.

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Recreational water can be contaminated with pathogens and chemicals that cause various illnesses, including gastrointestinal, skin, ear, respiratory, eye, neurologic, and wound infections. Some common pathogens found in recreational water include:

“Hot tub rash,” also caused by pools and lakes, results from contaminated water that stays on skin for an extended time. The germ that causes contamination is called Pseudomonas aeruginosa and originates in water that is not properly disinfected with chlorine or falls outside of the recommended pH level of 7.2–8.

Shingella germs come from fecal matter such as diarrhea and is spread by swimming in, or swallowing, contaminated water. It can also be spread by encountering fecal matter in other ways, such as through changing diapers, sexual contact, or eating food prepared by someone who has a Shingella infection.

How can waterborne illnesses be prevented?

The CDC recommends that individuals prevent waterborne illnesses at home, and while camping, hiking, and traveling, and backpacking by practicing safe measures like keeping water infrastructure maintained and treating and purifying water correctly. Waterborne illnesses can be prevented at industrial and commercial levels by implementing safety standards

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Burden of waterborne disease in the United States
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National Outbreak Reporting System
Last updated

Estimates are not actual values. For each waterborne illness in the study, reported illness data was corrected for underdiagnosis and underreporting. The data was adjusted to account for domestic cases only. To calculate deaths, the study applied an uncertainty model to generate a 95% credible interval with upper and lower limits centered around a point estimate. The full study methodology is here.