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Protecting your pool against pathogens

Swimming Pool Water Safety


Must-Know Myths (and Truths) About Maintaining A Healthy Pool

Ready for a quiz? Let’s see how much you know about swimming pool health and safety:

  1. True or False?: Chlorinated pool water is safer/cleaner than untreated recreational water (i.e. lakes and oceans)
  2. True or False?: Chlorine kills germs instantly.
  3. True or False?: A strong chlorine smell indicates a clean pool.

Unfortunately, all of three of these notion are false! Each of these are common myths that can lead to very serious health consequences. We’re here to debunk these rumors and help you pool your resources (if you will…) so you can make the most of the summer this year.

Common Causes of Swimming Pool-Related Illnesses:

We’ve previously addressed that there are a variety of possible waterborne pathogens that could be lurking in your drinking water–but, did you know that the same might be true in you pool? Despite popular belief, even chlorinated pools can harbor a multitude of dangerous bacteria, viruses, and protozoa. The most common causes of recreational water illnesses include:

  • Cryptosporidium
  • Giardia
  • Shigella
  • Norovirus
  • E. coli O157:H7
  • The saliva, blood, mucus, or skin of infected swimmers can directly contaminate pool water with enough pathogens to infect other swimmers. The largest concern however, is fecal contamination, due to the high concentration of pathogens in feces (which can be as high as one million per gram).

    Swallowing even a single mouthful of water contaminated with these germs can make you (very) sick. If infected with contaminated pool water, each of these pathogens carry with them a unique set of symptoms–ranging from skin, eye, ear, neurologic, or wound infections. However, one of the most common results is diarrheal illness.  

    While you may think that chlorine in your pool would kill these germs, it's really good pool health that keeps pathogens away. A recent study found that pool-related outbreaks largely outnumber outbreaks associated with untreated drinking water.

    What’s worse is that pool-related illnesses are on the rise. Outbreaks of Cryptosporidium infections linked to swimming pools have more than doubled from 2014 to 2016.

    Top 3 Myths About Chlorine in Pools:

    Let’s start by debunking an all-too-popular myth: Sufficient chlorine eliminates all germs instantly. There are two issues with this statement:

    1. There are many pathogens known to cause disease that are tolerant to chlorine (to varying degrees). For example, giardia–which is moderately resistant to chlorine–may survive for up to 45 minutes. Cryptosporidium, on the other hand, is extremely tolerant to chlorination and may survive up to 10 days in properly treated water!
    2. Chlorine disinfection does not occur immediately. It can take anywhere from minutes to even days in order for chlorine to effectively eliminate pathogens.

    Another lesser known issue surrounding chlorine is the issue of chlorine poisoning. Determining the proper amount of chlorine in a pool is delicate balancing act. Too little, and the chlorine won’t effectively disinfect the pool water. Too much, and you may beat risk of toxic exposure. Symptoms depend on which form of chlorine you came into contact with (liquid or gas), along with time of exposure. Typical symptoms of chlorine poisoning include:

  • Burning pain
  • Skin redness
  • Blisters
  • So, if too little chlorine is ineffective at removing germs and too much chlorine can be toxic….what’s the amount?

    The CDC recommends pool chlorine levels of at least 1 part per million (ppm), and 3 ppm for hot tubs. At this level, chlorine will eliminate most germs in less than an hour (assuming other factors, like pH and temperature, are in the recommended range).

    Another myth about chlorine–that a strong chlorine smell indicates clean water–is one of the largest pool-related misconceptions. We hate to be the bearers of bad news, but not only is this notion not true, it is very much the opposite. A healthy, clean pool should not smell.  A chlorine smell means you need to ADD chlorine.

    How is this possible? Well, that quintessential “pool smell” is due to chloramines–not chlorine. Chloramines can form when free chlorine gets into contact with ammonia and nitrogen mixes with chlorine. These compounds are found in natural body oils, sweat, personal care products, urine, fecal matter, and of course, the atmosphere–meaning that rain, especially in smog-prone areas, can increase chloramines in your pool.

    Tap Score Water Testing

    When chloramines are formed, this indicates that chlorine is “tied up” in the chloramines, rather than existing as free chlorine. Free chlorine is the form of chlorine that is able to protect against germs (for you chemistry interested folks, this is the sum of hypochlorous acid and hypochlorite that forms when you add chlorine to water). Chloramine can also kill germs, but it is way less effective compared to free chlorine.


    The best way to limit the formation of chloramines (and therefore reduce that “pool smell”) is to keep your pool covered when you’re not using it and shower before you dive in. We’ve all heard this before. It’s not just a mere suggestion–it’s a crucial step we can all take in order to protect our friends, family, and ourselves.

    With these debunked myths in mind, it is crucial to routinely monitor the chlorine concentrations in your pool and adjust the levels accordingly. You should test your pool at least once per week, and more frequently during heavy use months The CDC recommends  public pools be tested twice per day, but this may be unrealistic for you and your pool at home, especially if you take good care of it.

    Changes in factors such as water temperature and pH directly impact both the concentration and effectiveness of chlorine disinfection. In fact, chlorine can dissipate in just a matter of hours after addition on particularly hot days.

    The Importance of pH:

    Chlorine is not the only player in the world of pool-disinfection. Keeping pH levels in check are also vital to ensure a healthy pool environment. The CDC swimming pool pH between 7.2-7.8 (when chlorine is at least 1 ppm). Maintaining the pH level is important for several reasons. In addition to being the optimal range for disinfection, pH levels outside of 7.2 to 7.8 can cause eye and skin irritation.

    Ways to Stay Safe This Summer:

    Hopefully with our myth debunking you can make informed choices before you dive in head first. A few good practices to follow when it comes to pool safety include:

  • Not swimming when sick with diarrhea
  • Not swallowing pool water
  • Shower before and after swimming
  • Unfortunately, a survey by the Water Quality and Health Council uncovered that one in four adults said they would swim within an hour of having diarrheas. Don’t be that person, please.

    If a pool is contaminated, the CDC recommends closing it immediately and treating it for multiple hours of “hyperchlorination”–a water treatment process that involves adding a high dose of chlorine in order to disinfect the water.

    A CDC report uncovered some unsettling statistics about pool safety––in one study, 78.9% of routine public pool inspections identified at least one violation. Additionally, one in eight of those inspections revealed a violation severe enough to require that the pool close immediately. 

    We encourage you to learn about your own pool’s heath–so you, too, can have a happy and healthy summer of swimming!

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    About The Author


    Kate leads operational strategy as COO at Tap Score and SimpleLab. She oversees daily, as well as long-term logistics for tens of thousands of environmental samples across hundreds of certified laboratories. However, she started her environmental testing career by way of scientific blog writing at Tap Score and it continues to be one of her favorite aspects of the business. Outside of Tap Score, Kate loves making homemade pasta, floral arranging, and singing along to Dolly Parton tunes.
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