WARNING!
This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.
By Dr. Mercola
If you’re planning to visit a public pool this summer, the U.S. Centers for Disease Control and Prevention’s (CDC) annual report may make you think twice.1 More than 48,600 public pools, hot tubs and water playgrounds were tested, and close to 80 percent had at least one safety or hygiene violation.
One in 8 of the pools was so dirty that it had to be closed immediately after inspection. Pools meant for young children and infants were especially risky, with 1 in 5 being closed right after inspection. Michael Beach, Ph.D., the CDC’s associate director for Healthy Water, said:2
“This is particularly troubling because children who are still learning their toiletry skills are more likely to contaminate the water, and more likely to swallow the water, both of which can lead to diarrheal illness.”
Most Common Violations at U.S. Public Pools
About one-third of local health departments do not monitor or inspect public pool facilities, so virtually anything could be lurking in the water. Most often, violations were related to:
- Improper pH (15 percent)
- Safety equipment (13 percent) — especially in order to prevent drowning
- Disinfectant concentration (12 percent) — especially too little disinfectant
A past CDC study also revealed that feces frequently contaminate pool water. Fifty-eight percent of the pool filters the CDC tested in 2013 were found to contain E. coli bacteria. According to the CDC:3
“Finding a high percentage of E. coli-positive filters indicates swimmers frequently contaminate pool water when they have a fecal incident in the water or when feces rinse off of their bodies because they do not shower thoroughly before getting into the water.”
Pseudomonas aeruginosa, another type of bacteria that may cause ear infections and rashes, was found in 59 percent of pool filters tested. Norovirus, giardia and shigella are other illness-causing microbes that may be found in public pools. There’s also cryptosporidium, or crypto, a parasite that can cause diarrhea.
Ninety crypto outbreaks were reported from 2011 to 2012, and most occurred in treated water, such as pools, spas and hot tubs (crypto is resistant to many common disinfectants).4
In order to combat the increasing rates of infection with cryptosporidium, which is now the leading cause of swimming pool-related outbreaks of diarrheal illness, the CDC recommends supplementing disinfection at public pools and hot tubs with ultraviolet light or ozone.
If You Can’t See the Drain, Don’t Jump In
Experts recommend swimmers use common sense before jumping in to public pools, including gauging the cloudiness of the water.
If it’s so cloudy you can’t see the drain at the bottom, don’t jump in the pool (if the water is this bad, the pool shouldn’t even be open, according to CDC’s Beach, so notify the management as well).
Other common sense measures include not swimming if you have diarrhea, taking frequent bathroom breaks (especially for children) and checking diapers every 30 to 60 minutes.
You can also pick up a container of water test strips at your local hardware store to test the pool water yourself. You’ll want to look for the following results, but keep in mind that even if these check out, there’s still a risk from crypto and disinfection byproducts (DBPs), which are discussed below:5
- Free chlorine concentration of at least 1 part per million (ppm) in pools and at least 3 ppm in hot tubs
- Free bromine concentration of at least 3 ppm in pools and at least 4 ppm in hot tubs
- PH levels between 7.2 and 7.8
Dangerous Compounds Form When Chlorine Mixes With Pee, Poop, Sweat, and Dirt
Have you ever wondered why it’s recommended that you shower just before entering a public pool? According to the CDC:6
“The job of pool chemicals is to kill germs. But when pee, poop, sweat and dirt rinse off our bodies and into the pool water, the chemicals break down these other things instead of killing germs. This uses up the chemicals’ power, which means there’s less to kill germs.”
This is only one of the issues with such “organic matter” in pools, however. Highly toxic DBPs form from reactions between pool disinfectants and organic matter, including hair, skin, sweat, dirt and urine.
In one study, researchers mixed uric acid from human urine with chlorine and found it creates two DBPs: cyanogen chloride (CNCl) and trichloramine (NCl3).7 The former, CNCI, is classified as a chemical warfare agent and is a known toxin to your lungs, heart and central nervous system. NCl3 is linked to lung damage.
As for how dangerous this is, practically speaking, the researchers found that, in a worst-case scenario, urine in a pool might lead to about 30 parts per billion (ppb) of cyanogen chloride, which is well below the 70 ppb used as the maximum cyanogen concentration allowed in drinking water, according to the World Health Organization (WHO).8
Cyanogen chloride leads to coma, convulsions and death only at much higher levels (about 2,500 ppb), an amount that would be difficult, and probably impossible, to generate in a typical swimming pool from urination alone.9
This doesn’t mean that smaller doses are “safe,” however, as DBPs have been linked to serious health problems at levels found in swimming pools.
DBPs May Cause Cancer
No one wants to spend a day at the pool and come home with a bad bout of diarrhea or other gastrointestinal illness. However, you should know that even if you avoid getting acutely ill, there are long-term risks to consider. Spending just 40 minutes in a chlorinated pool has been linked to DNA damage.10
This is not due to the chlorine itself but due to the DBPs. Trihalomethanes (THMs), one of the most common classes of DBPs, are Cancer Group B carcinogens, meaning they’ve been shown to cause cancer in laboratory animals.
They’ve also been linked to reproductive problems, such as spontaneous abortion, stillbirths, and congenital malformations, in both animals and humans, even at low levels.
The cancer risk of DBPs (in this case THMs) is greatest from skin exposure while swimming (compared to gastrointestinal exposure, such as would occur from drinking water).11
This may explain why people who frequent swimming pools have an increased risk of bladder cancer compared to those who do not.12
Why Public Pools May Cause Respiratory Symptoms
Respiratory issues, such as allergies and asthma, are sometimes associated with the chlorine at public pools, but many of the health risks associated with swimming in chlorinated water are actually related to toxic DBPs:
- Swimming instructors are more than twice as likely to suffer frequently from sinusitis or sore throat, and more than three times as likely to have chronic colds, than pool workers with less DBP exposure, such as catering employees or receptionists.13
- Compared to the general population, pool workers with high levels of exposure were at a 40 percent greater risk for tightness of the chest and were over 700 percent more likely to suffer breathlessness while walking.14
- DBPs may cause weakening of your immune system, disruptions to your central nervous system, damaging effects to your cardiovascular system, unhealthy functioning of your renal system and harmful impacts to your respiratory system.
How to Safely Enjoy Swimming This Summer
Swimming is an excellent pastime, both for physical activity and emotional relaxation and enjoyment. If you have the option, swimming in an ocean is an excellent alternative to swimming in a pool, as is swimming in a lake or other natural unpolluted body of water.
If you have a pool in your backyard, you can also find a way to keep your pool clean from bacteria, algae, and other organisms without the use of dangerous chemicals.
One of the best solutions is to not chlorinate your pool and just use a maintenance "shock" treatment every five or six days, which will kill the algae buildup. The shock treatment volatilizes in about 24 to 48 hours and gives you a several-day window in which you can safely use your pool.
You can also reduce the amount of organic material you bring into the pool, and thereby the amount of DBPs created, by showering prior to entering and teaching your children not to urinate in the water.
This will be difficult if you're visiting a public swimming pool or waterpark, however, since many people do not shower prior to entering, and you can't control what other types of compounds (from personal care products, sunscreens, insect repellants and, yes, urine and feces) might be in the water.
An occasional trip to a well-maintained public pool likely poses a low risk for most people. Your risks may be increased in indoor settings, including indoor waterparks. The indoor setting allows DBPs to concentrate in the air, especially during colder months when fresh air from outdoors is not circulated. In the largest outbreak to date, which occurred in 2007, at least 665 people became ill from DBPs at an indoor waterpark facility.15
Further, disease outbreaks, especially those involving crypto, affect young children most often.16 So in addition to reconsidering the use of indoor facilities, you may want to reconsider bringing very young infants into any public pool.