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Why Do Swimming Pools Need Chlorine?

Why Do Swimming Pools Need Chlorine?

Most of us are used to the idea that swimming pools need chlorine. We know that it keeps the pool clean, but we also know that there are downsides. It is common knowledge that too much chlorine can produce an unpleasant chemical odor, make your skin irritated, cause red eyes, and even dye your green. But what if we told you that none of those symptoms are the result of too much chlorine in the water? The fact is, chlorine is a widely misunderstood chemical. Its role in swimming pool sanitation is critical, and when used correctly it is actually completely safe.

Why Do Swimming Pools Need Chlorine [infographic]

How Does Chlorine Keep a Pool Clean?

Swimming pools need chlorine to keep the water clean and safe to swim in. Chlorine helps keep water clean by preventing the growth of algae. It keeps your pool water safe by attacking and neutralizing harmful bacteria and microorganisms.

The magic of chlorine is in a simple chemical reaction. Once the chlorine solution is in your pool water, it breaks down into two critical molecules, hypochlorous acid and hypochlorite ion. Both chemicals work by attacking and breaking down the lipids in the cell walls of microorganisms, killing them and rendering them harmless. While both chemicals work, hypochlorous acid is much faster. It can oxidize an organism in just seconds. Hypochlorite ion can take as long as 30 minutes. Both chemicals are vital to the hygiene of your pool.

Pool Chemistry is Critical to Pool Hygiene

Maintaining good pool chemistry is the only way to keep your pool clean. The most significant factor in pool water safety is its pH level. The human body maintains a pH level of 7.4. The pH of your pool water should remain between 7.2 and 7.8. At those levels, the water will not irritate the skin, eyes, or mucous membranes. That is also the ideal pH for chlorine. If the pH is too high, there won’t be enough hypochlorous acid. Since hypochlorous acid is the fast-acting oxidizer, a pool with a high pH will take much longer to get clean.

After pH, the second most significant factor in the safety of your pool water is the free chlorine level. Swimming pools need chlorine at the right levels to stay clean. The Centers for Disease Control and Prevention (CDC) recommends a free chlorine level of 1-3 ppm for a pool and 2-4 ppm for a hot tub or spa. You should test your pool at least 2-3 times a week to check pH and chlorine levels, and adjust as necessary.

How Much Chlorine is Necessary?

We know that swimming pools need chlorine. How much and how often you will need to add chlorine depends on how your pool is used as well as environmental factors. The rate at which chlorine is used up in your pool is called chlorine demand. Some chlorine is used up as it reacts with microorganisms and oxidizes them. But chlorine can also be used up when it reacts with other contaminants that are brought into the pool by unhygienic swimmers. Contaminants such as sunscreen, body lotion, and hair products add to chlorine demand. Human contaminants such as sweat, body oil, and urine also increase chlorine demand.

Swimmers can help reduce chlorine demand by showering before entering the pool and not peeing in the pool. Children should take regular breaks from swimming to use the restroom, and any diapers should be changed away from the pool to avoid contamination.

Even without any swimmers, swimming pools need chlorine added regularly, since the sun also breaks down free-chlorine. One simple way to reduce the effects of the sun on your free chlorine levels is to use a solar pool cover that blocks out UV rays. You can also use chlorine with added cyanuric acid, a stabilizer that reduces the effects of the sun. Without it, UV rays can break down the hypochlorite ion, allowing the chlorine to evaporate. With cyanuric acid, the hypochlorite ion is stabilized and won’t break down as fast. However, stabilizer can reduce the speed at which hypochlorite oxidizes microorganism. That’s ok in a large pool as long as you keep free chlorine levels in check. However, stabilizer should never be used in a hot tub or spa.

No, Your Pool Doesn’t Have Too Much Chlorine

As chlorine reacts and combines with unwanted contaminants, it forms compounds called chloramines. Chloramines, not chlorine, are responsible for the odor that many swimmers incorrectly associated with chlorine. Chloramines are also irritants that are mostly responsible for red eyes and itchy skin. The odor and irritation are signs that chlorine is quickly being converted to chloramines and the pool actually needs more chlorine, not less.

Irritation is also a sign of pH that is too high or too low, which can also affect free chlorine levels. So if a pool smells like chemicals and is causing irritation, it’s time to check the water and rebalance it.

Another symptom incorrectly attributed to chlorine is green hair. In fact, green hair is not the result of chlorine. The green color comes from copper that bonds to the proteins in the hair. Copper in pool water has two sources. One source is algicides. Many algicides contain copper, which is good for preventing algae growth but bad for your hair. Another source of copper in a pool is copper from pool-fittings that is dissolved into the pool water when the pH is too high. So if you aren’t using copper-based algaecide and your swimmers’ hair is turning green, check your pH.

What Are the Risks of Chlorine?

Chlorine in its pure form is highly toxic, and its fumes can be hazardous to your health. However, chlorine that is dissolved in a pool at the appropriate levels poses no threat whatsoever. In fact, chlorine is added to drinking water for the same reason it is added to pool water, to break down harmful microorganisms. EPA guidelines allow for chlorine levels up to 4 ppm in tap water, but in a properly maintained pool, free chlorine levels should be 1-3 ppm. In other words, there is less chlorine in a properly maintained pool than in safe drinking water.

The main danger of chlorine is to the person handling the chlorine and adding it to the pool. Chlorine can be added to the pool as sticks, pellets, or in liquid form. To use chlorine safely, make sure to follow the manufacturer’s directions. Avoid inhaling fumes and always keep chlorine and other pool chemicals out of reach of children. Never mix different types of chlorine and don’t buy more than you can use in a season since chlorine will lose its effectiveness over time. Typically, swimming pools need chlorine that is under a year old.

What are the Benefits of Chlorine?

The benefits of chlorine are immense. Just think about the diseases that humans faced, and still face, in the absence of clean drinking water. Swimming pools need chlorine because chlorine is the only effective way to keep pool water clean. Even a saltwater pools need chlorine (they just generates the chlorine themselves). While there are other methods of cleaning pool water, such as UV or ozone treatment, they are not replacements for chlorine. Other treatments can clean water before it enters the pool, but do nothing to maintain the hygiene of the water once it is in the pool. Bathers are continually introducing new contaminants, and only chlorine has the residual effect of cleaning pool water as the contaminants are introduced.

Without chlorine, harmful bacteria can cause infections and illness. Microorganisms in pool water can cause gastrointestinal, skin, ear, respiratory, eye, neurologic, and wound infections. According to the CDC “the most commonly reported [disease] is diarrhea, caused by germs like Cryptosporidium(“Crypto”) and E. coli 0157:H7.” If that sounds unappealing, you definitely want to swim in chlorinated water.

However, chlorine doesn’t kill bacteria instantly, so it is still important to practice basic hygiene. Always bathe before swimming, and make sure to rinse off all soaps, shampoos, and conditioners. Bathe again right after swimming. Never go into a pool if you have diarrhea and never allow yourself or a child to relieve themselves in a swimming pool.

Keeping Your Pool Clean the Easy Way

If you want to make sure your pool water is always clean and safe to swim in, The Pool Butler can help. Swimming pools need chlorine and pH levels maintained over time. Our regular maintenance service will ensure that your water is always balanced. You never have to worry about the safety of your family and guests. All you have to do is enjoy your pool. Contact us today to learn more.



“Water, Sanitation & Environmentally-Related Hygiene.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 17 June 2014,

“National Primary Drinking Water Regulations.” EPA, Environmental Protection Agency, 22 Mar. 2018,

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