Frequently Asked Questions

Image of a sink faucet dripping water

Q: What are the main findings?

A: In 2014 in the United States, 17 waterborne pathogens caused an estimated 7.15 million illnesses, 601,000 emergency department visits, 118,000 hospitalizations, and 6,300 deaths. They incurred $3.3 billion in direct healthcare costs, which includes insurance and out-of-pocket payments.

Otitis externa (“swimmer’s ear”) and norovirus infection were the most common illnesses. Most of the hospitalizations and deaths were caused by three diseases: nontuberculous mycobacterial infection, Pseudomonas septicemia and pneumonia, and Legionnaires’ Disease. The germs that cause these diseases live in pipe slime, also known as biofilm. These serious respiratory illnesses cost $2.39 billion annually.

The estimates include illnesses that occurred from drinking, recreational, and environmental water exposures. The analysis highlights the expanding role of environmental germs in causing respiratory illness. These germs can grow in drinking water distribution systems; pipes inside of homes and buildings; recreational water venues (such as, hot tubs); and industrial water systems, such as cooling towers. However, the risk still exists for getting a gastrointestinal illness from germs spread through water.

Q: Why do we call these estimates?

A: We say estimate because the reporting systems and surveys used to gather information provide vital data, but do not capture every illness. We use the best data available and make reasonable adjustments—based on surveys, study results, and statistical methods—to account for missing pieces of information (for example, the fact that only a fraction of all illnesses are diagnosed and reported).

Q: Why don’t the estimates include illnesses caused by toxins and chemicals in water?

A: The potential health outcomes for illnesses caused by some toxins and chemicals in water (for example, lead) take a longer time to appear. This report focused only on infectious diseases for which data were available. Analyses for short-term health outcomes of illnesses caused by infectious diseases, like the ones in this report, are different than analyses for chronic illnesses that take a longer time to develop. There is evidence that exposure to toxins, like those produced by harmful algal blooms (HABs), and chemicals — like per- and polyfluoroalkyl substances (PFAS) — can lead to adverse health effects, but they were not a part of this analysis.

Q: How many illnesses are linked to drinking water? Swimming/recreational water? Private wells?

A: CDC’s estimates calculated the total impact of disease from any type of water exposure. Although some illnesses in this analysis are more commonly spread through drinking or swimming in contaminated water, we cannot say for certain which type of water exposure caused the illnesses in this paper. In the future, we hope to estimate the impact of specific types of water exposure to the overall burden of waterborne disease.

Q: Why are the estimates not available by state or county?

A: The data sources are different for each illness. Most lack the information needed to estimate illnesses by state or county.

Q: What are biofilm-associated germs?

A: Sometimes waterborne germs live together in a group, known as a biofilm. A biofilm is a group of microorganisms—often a mix of bacteria, fungi, and amebas—that live together and release a slimy, glue-like substance, which allows them to stick to surfaces. This slimy “home” acts as a barrier to water treatment chemicals, like chlorine, helping the germs survive and multiply.

A biofilm is more likely to grow abundantly in places where water does not move, such as the inner surfaces of water pipes, water storage tanks, or water heaters.

Some potentially harmful germs that can grow and multiply in your home’s water system (and the types of illnesses they cause) include: nontuberculous mycobacteria (lung, blood, or skin infection); Legionella pneumophila (lung infection); Pseudomonas aeruginosa (blood, lung, or skin infection); Naegleria fowleri (brain infection); and, Acanthamoeba spp. (brain and eye infection).

When you turn on the water, particularly if water has remained stagnant in your home’s pipes for longer than normal (for example, a week or more), germs from biofilm can come out of the faucet, showerhead, or other water devices. Some of these germs can make people sick when the water:

  • Is inhaled as a mist
  • Comes in contact with an open wound
  • Goes up the nose (for example, when using a neti pot)
  • Is used to rinse or store contact lenses, or is splashed in your eyes while you are wearing contacts

Most healthy people exposed to water that contains these germs do not get sick. However, there are certain groups of people who are more at risk for illness, such as individuals who are older than 50, are current or former smokers, have an underlying lung condition or a weakened immune system.

More information on biofilm-related germs can be found on the Preventing Waterborne Germs at Home webpage.

Q: What is CDC doing to help prevent illnesses spread through water?

A: CDC works to prevent, control, and monitor water-related illnesses and outbreaks. Understanding the causes of these illnesses is critical to guiding science-based interventions and addressing new and growing problems. CDC’s waterborne disease prevention work includes researching health impacts; tracking disease; developing new laboratory methods and materials; communicating to policymakers and the public; sharing information; and working with partners.

Specific examples include the following:

  • Supporting state and local health departments to detect, investigate, and control waterborne infections and disease outbreaks;
  • Providing national leadership for the prevention of recreational water illnesses through the Model Aquatic Health Code (MAHC);
  • Assisting with water-related emergencies and outbreaks;
  • Educating the public on how to prevent waterborne diseases;
  • Developing new technologies, such as whole genome sequencing, for detecting and analyzing pathogens;
  • Developing water management plans in large buildings, such as healthcare facilities, to prevent infections caused by biofilms in the plumbing; and,
  • Researching the emergence of antibiotic-resistant germs in drinking water and wastewater.

Learn more at

Q: Why didn’t CDC use surveillance data for all of the pathogens?

A: Surveillance data are not available for all of the pathogens. For example, although some surveillance for nontuberculous mycobacteria infections exists in a few locations, it is not available nationwide.

Q: When will the next estimate of waterborne illness be done?

A: CDC plans to update its estimates regularly.