Yes, you can get sick from swimming in a public pool, which is why health officials track Recreational Water Illnesses (RWIs). These illnesses are caused by germs spread when people swallow, have contact with, or breathe in mists from contaminated water. Pathogens are not always eliminated by the pool’s disinfection system. Public pools are shared environments where human waste, sweat, and other bodily fluids interact with the water chemistry. Understanding the infectious agents and chemical irritants present is the first step toward minimizing your risk.
Infectious Agents in Pool Water
The most common pathogens responsible for RWIs cause gastrointestinal illness, primarily spread through accidental water ingestion. One major concern is the parasite Cryptosporidium (“Crypto”), which causes watery diarrhea, cramps, and nausea. This protozoan is problematic because its tough outer shell allows it to survive in properly chlorinated pool water for up to 10 days, making it highly resistant to chlorine. A single diarrheal incident from an infected person can introduce millions of oocysts into the water, and a small number is enough to cause infection.
Another common intestinal parasite is Giardia, which also causes diarrheal disease and is transmitted similarly to Cryptosporidium. While Giardia is more susceptible to chlorine, it can still survive in pool water longer than common bacteria. Bacteria like Escherichia coli (E. coli) and viruses such as norovirus and adenovirus can also contaminate pool water through fecal matter, leading to gastrointestinal and respiratory symptoms.
The bacteria Pseudomonas aeruginosa thrives in warm, wet environments and frequently causes non-gastrointestinal illnesses. This organism is known for causing “hot tub rash,” characterized by itchy red bumps, and is a common culprit behind swimmer’s ear, an infection of the outer ear canal. While chlorine is effective against many germs, these pathogens remain a threat when disinfection is compromised or a chlorine-resistant organism is present.
How Illness Spreads and Chemical Irritants
The primary mechanism for contracting an RWI is the accidental swallowing of contaminated water, which can happen even in small amounts. Contamination usually starts when an infected person enters the water with microscopic fecal matter on their body. If that person has diarrhea, the risk of pathogen spread increases dramatically, introducing a high concentration of germs into the shared water.
Illness can also be caused by chemical irritants that form when disinfectants react with substances swimmers bring into the pool. The strong “pool smell” often associated with a heavily chlorinated pool is actually a sign of poor water quality, not strong chlorine. This odor is caused by chloramines, chemical byproducts that form when active chlorine reacts with nitrogen-containing compounds like sweat, urine, and cosmetics.
Chloramines are poor disinfectants and greatly reduce the effectiveness of the pool’s free chlorine, allowing pathogens to survive longer. Chloramines off-gas into the air above the water, especially in indoor pools, where they can irritate the eyes, skin, and respiratory tract. Swimmers may experience red, stinging eyes or coughing because of these airborne irritants, confirming that the pool’s water-to-swimmer waste ratio is too high.
Practical Steps for Safer Swimming
The most effective way to reduce the risk of illness is to adopt healthy swimming habits that minimize the introduction of contaminants. Always shower thoroughly with soap and water before entering the pool to remove sweat, dirt, and any trace of fecal matter. This simple action significantly reduces the formation of irritating chloramines, helping the chlorine work more effectively against germs.
Never swim if you have diarrhea or have been sick, and keep children with diarrhea out of the pool. If diagnosed with an infection like cryptosporidiosis, wait for at least two weeks after symptoms stop before returning to the water. Children in diapers should be checked frequently, ideally every hour, and their diapers should be changed in a bathroom, away from the poolside.
Avoid swallowing the pool water, even a small amount, as ingestion is the primary route of infection for gastrointestinal RWIs. Perform a quick check of the pool environment: if the water is cloudy or you notice a strong chemical odor, this indicates that water quality may be compromised by high chloramine levels. Taking frequent restroom breaks and encouraging children to do the same also helps keep contaminants out of the water.