Why Can I Smell Chlorine at Public Pools but Not In My Private Pool?
The scents of summer can bring back all kinds of fond memories. But, "the smell of chlorine" can actually signify a number big problems for swimmers.
"Pool smell" is caused by chloramines, not chlorine. Chloramines are the chemical compounds that build up in pool water when it is improperly treated. They result from the combination of two ingredients: (a) chlorine disinfectants and (b) perspiration, oils, urine, and other bodily fluids that enter pools on the bodies of swimmers. Chlorine disinfectants are added to pool water to destroy germs that can give swimmers diarrhea, ear aches, burning eyes, difficulty breathing, and athlete's foot. Perspiration, oils, fecal matter, and urine, however, are unwanted additions to pool water. By showering before entering the pool, and washing these substances from the skin, swimmers can help minimize pool smell.
The American Chemistry Council wrote an amazing article that breaks down the Chemistry of Pool Smell. Here is an excerpt from that article:
The Chemistry of Pool Smell
When chlorine disinfectants are added to water, two chemicals are unleashed that destroy water borne germs, algae, and bacteria: hypochlorous acid, HOCl, and hypochlorite ion, OCl-. A measure of the chlorine in these two chemicals is known as "free available chlorine" or FAC. Pool operators manage the FAC level of pool water for the safety of swimmers. Their challenge comes from the fact that FAC is reduced when it reacts with perspiration, oils and urine from swimmers to form chloramines.
One way that chloramines are formed in pool water is by the reaction of hypochlorous acid with ammonia. Ammonia, NH3, is a component of sweat and urine.
There are three chemical reactions that can occur when hypochlorous acid reacts with ammonia, each involving the replacement of hydrogen ions with chlorine ions. When one of ammonia's hydrogen ions is replaced with chlorine, monochloramine is formed:
HOCl + NH3 → NH2Cl + H2O
Replacing one more hydrogen ion with chlorine produces dichloramine,
HOCl + NH2Cl → NHCl2 + H2O
Finally, it is possible to replace all three of ammonia's hydrogen ions with chlorine to form trichloramine, also known as nitrogen trichloride:
HOCl + NHCl2 → NCl3 + H2O
Monochloramine is sometimes intentionally added to water because it is actually a useful disinfectant. Drinking water, for example, is sometimes purified with monochloramine. Dichloramine and especially trichloramine are the chloramines most responsible for pool smell.
Managing Chlorine in the Pool
As hypochlorous acid combines with ammonia to form chloramines, the FAC of pool water is reduced. Lowering the FAC reduces the ability of chlorine to destroy germs. The amount of chlorine that is "tied up" in chloramine compounds, and is therefore unavailable as free chlorine, is known as combined available chlorine (CAC). The sum of FAC and CAC is the total chlorine (TC).
TC = FAC + CAC
The Association of Pool and Spa Professionals suggests FAC concentrations in pool water should remain in the range 1.0 - NC 4.0 parts per million for chlorine to work effectively (FAC should never fall below 1 part per million). CAC levels should be less than 0.2 parts per million.
Pool managers can use test kits to measure both FAC and TC. CAC is then simply calculated:
CAC = TC - FAC
Minimizing Pool Smell
Swimmers with reddened, irritated eyes have been known to complain that "there is too much chlorine in the pool". In fact, however, when pool water is irritating, there is not enough chlorine in swimming pool water!
You may be surprised to learn that there is no odor to a well-managed pool. Chloramines, which produce pool smell, can be eliminated using chlorine. "Shock treatment" or "superchlorination" is the practice of adding extra chlorine to pools to destroy ammonia and the organic compounds that combine with chlorine to make chloramines. To effectively destroy chloramines through shock treatment, the pool water FAC concentration must be about ten times the CAC.
According to the Centers for Disease Control (CDC), breathing in or coming into contact with chloramines at the places we swim can lead to negative health effects in swimmers and others in the swimming area, including:
Everyone (swimmers and others in the swimming area)
Respiratory symptoms such as nasal irritation, coughing, and wheezing. Asthma attacks can be triggered in people who have asthma.
Red and itchy eyes.
Skin irritation and rashes.
What can I do to reduce chloramine formation?
We all share the chlorinated water we swim in and the surrounding air we breathe. Here are a few simple and effective steps swimmers can take to help protect our health and the health of our family and friends:
Keep pee, poop, sweat, and dirt out of the water!
Never swim or let your kids swim if sick with diarrhea.
Use the toilet before getting into the water.
Shower before getting into the water. Rinsing off in the shower for just 1 minute removes most of the dirt or anything else on your body.
Wear a bathing cap while in the water.
Never pee in the water.
Take a break—every hour!
Take kids on bathroom breaks.
Check diapers and change them in a bathroom or diaper-changing area to keep pee and poop out of the water.
Talk to others.
Tell other swimmers and parents of young swimmers about chloramines and the steps they can take to help prevent them.
Encourage pool operators to take steps known to prevent and get rid of chloramines.
Tell the lifeguard or pool operator immediately if you or your family or friends:
See poop in water;
Smell chemical odors in the swimming area; or
Experience respiratory, eye, or skin irritation that could be linked to the water or the air surrounding the water.