Q: Why is chlorine added to swimming pools and spas?

A: Chlorine kills harmful microorganisms that can cause health-related problems in swimming pools and spas. Chlorine-based swimming pool and spa disinfectants help prevent swimmers’ ear, athlete’s foot, skin rashes and diarrhea. Legionnaires’ Disease and Pontiac Fever can also be prevented with proper chlorination, particularly in the hot tub and spa environment. The U.S. Centers for Disease Control and Prevention (CDC) calls chlorine and proper pH, “the first defense against germs that can make swimmers sick.”

Q: How is chlorine added to swimming pools and spas?

A: Chlorine may be added to pools in a variety of forms, including chlorine gas, liquid sodium hypochlorite solution ( bleach) or dry calcium hypochlorite granules or tablets. When added to water, each of these products unleashes the power of chlorine chemistry to destroy disease-causing germs. Studies show that another form of chlorinated disinfectant—chlorinated isocyanurates—have a special advantage in controlling germs in outdoor swimming pools. Chlorinated isocyanurates, known as “stabilized chlorine,” release the disinfecting power of chlorine slowly, in a “time-release” manner. This property makes them resistant to UV radiation from the sun, a plus for swimmers’ health. Some pools are equipped with chlorine generators that produce free chlorine directly in the pool water by applying electricity to salt.

Q: What are the advantages of using chlorine to disinfect pools?

A: The U.S. Centers for Disease Control & Prevention (CDC) calls chlorine and pH “the first defense against germs that can make swimmers sick.”

Chlorine is the disinfectant of choice for the majority of public pools and nine out of ten residential pools in the U.S. Chlorine levels are easy to monitor and can be adjusted based on pool conditions such as the number of swimmers in a pool. A major advantage is that chlorine provides a residual level that continues to protect long after it is applied. Disinfectants such as ozone and ultraviolet light can provide supplemental treatment to control chlorine resistant germs like Cryptosporidium. However, none of these technologies eliminates the need to maintain a proper chlorine levels in pool water.

Q: Why do some pools seem to use too much chlorine?

A: Swimmers often mistakenly blame red eyes, itchy skin and a strong chemical smell of pool water on “too much chlorine.” Generally, the odor and irritation they notice is not due to chlorine, but to chloramines, chemical compounds that build up in pool water when it is improperly treated. A properly managed pool has little odor.

Chloramines form when chlorine combines with ammonia and other compounds found in perspiration, urine, saliva, body oils and lotions that are brought into pools on the bodies of swimmers. Swimmers can help prevent chloramines forming in pools by showering before swimming. Pool managers can closely monitor and adjust pool chemical levels to minimize chloramines formation.

Unhealthy levels of chloramines can be treated with a high dose of chlorine, known as shock treatment. Shock dosing—conducted when swimmers are absent from the pool—destroys chloramines, organic contaminants, and a variety of germs.

Q: What are the signs of a “healthy pool?”

 A: The Healthy Pools partnership recommends you use your senses to help recognize the difference between a  healthy pool and a potentially risky one. What should you notice?

Sight: Look for water that’s clean, clear and blue. The painted stripes and drain should be clearly visible at the bottom of the pool.

Touch: Check for tiles that feel smooth and clean. Sticky or slippery tiles are caused by algae and other unwanted organisms.

Smell: Make sure there are no strong odors. Chlorine helps keep pools healthy, and will not cause a strong chemical odor in a well-maintained pool.

Sound: Listen for pool cleaning equipment. Properly running pumps and filters make sure that clean, disinfected water reaches all parts of the pool.

Taste: Never drink or swallow pool water. In fact, try to avoid getting it in your mouth at all.

Common Sense: Do your part to protect yourself and others. Always shower before you swim, and never swim when you are ill with diarrhea.

Q: How can I tell if my pool is properly treated?

A: You can check your pool chemistry by using a pool test kit or test strips. The  Healthy Pools website shows you how.

What can I do to help maintain a “healthy pool?”

The U.S. Centers for Disease Control and Prevention (CDC) has issued  Six "PLEAs" to promote Healthy Swimming:

Three "PLEAs" for All Swimmers—Practice these three "PLEAs" to stop germs from causing illness at the pool:

  1. Please don't swim when you have diarrhea. You can spread germs in the water and make other people sick. This is especially important for kids in diapers.
  2. Please don't swallow the pool water. In fact, avoid getting water in your mouth.
  3. Please practice good hygiene. Take a shower before swimming and wash your hands after using the toilet or changing diapers. Germs on your body end up in the water.

Three "PLEAs" for Parents of Young Kids—Follow these three "PLEAs" to keep germs out of the pool and your community:

  1. Please take your kids on bathroom breaks or check diapers often. Waiting to hear "I have to go" may mean that it's too late.
  2. Please change diapers in a bathroom or a diaper-changing area and not at poolside. Germs can spread to surfaces and objects in and around the pool and cause illness.
  3. Please wash your child thoroughly (especially the rear end) with soap and water before swimming. Everyone has invisible amounts of fecal matter on their bottoms that end up in the pool.

Q: Is swimming in an indoor pool unhealthy?

A: Medical experts agree that swimming is a healthy form of exercise for children and adults. For indoor pools, in addition to appropriate chemical treatment, proper ventilation is important to avoid the build-up of compounds like chloramines. Always  follow CDC recommendations when swimming and use your senses to check for the signs of a healthy pool.


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