Chlorine and Bacteria in Pools: You just can’t win.

Public pools hang in a delicate balance between fostering an environment for bacteria and being over chlorinated and posing severe chlorine-based health problems.

“Chlorine breaks down very fast in the presence of high contamination and swimmer load and due to the effects of the sun’s UV rays and heat.” (1) This can cause the pool water to be less effective in killing the pathogens which cause diseases like Gastroenteritis, Dysentery, Giardia, Dermatitis and more. (1)

Often pool caretakers overcompensate for this and thus over-chlorinate pools. When chlorine comes in contact with organic matter like dirt or leaves it can produce dioxins, furans and trihalomethanes. The International Agency for Research on Cancer are anticipated carcinogens which can build up in the bodies of a human. (2)

One study shows that there seems to be a strong correlation between children who swim very often in chlorinated pools and those children developing asthma. (3)

There has been a move to utilizing non-chlorine products to sanitize pools, including copper and silver which are known anti-bacterial and anti-viral instruments. (1)

I myself can remember jumping in a pool with a bunch of friends ‘just for fun’ after it was closed. It alarms me to learn that, due to chlorine degrading in the sun, pool caretakers put chlorine into pools at closing time so that the chlorine has time to circulate and become evenly distributed during the night.

I was unintentionally exposing myself to potentially high concentrations of chlorine, which can be toxic.

Perhaps more studies need to be done to determine an effective yet safer method of sanitizing pools.



9 Responses to Chlorine and Bacteria in Pools: You just can’t win.

  1. Terrance Morris says:

    I’ve done some work for the American Chemistry Council, and since we’re celebrating 100 years of chlorine, your post is quite timely. It’s true that exposure to the chemical itself can be dangerous, but it’s really been one of the most effective and safe ways to ensure water is safe for both consumption and play.

  2. reddecember says:

    Thanks for your comment! I suspect that chlorine in and of itself is safe, and wouldn’t be used if otherwise. Perhaps it is in user error and inappropriate use of chlorine where the dangers lie.

  3. baustin says:

    There’s some crazy stuff going on in public places. Do you know the actual chlorine concentrations people put into pools? You’d think it would still be at an “acceptable” level, even at its highest concentration level in a pool. Science is coming up with some interesting things lately, like how public drinking fountains contain more bacteria than a doorknob and other weird random facts like that. Thanks for your post.

  4. detheredge says:

    I have been one of those kids to, jumping in the pool after hours just to say you did. Maybe if we knew the things we did now, we would not have been little rish takers.

  5. Danny says:

    Seriously, there are safe pools and unsafe pools… there are risks associated with everything, chlorine included. But it’s important to keep in mind that the risks associated with swimming in untreated water are actually pretty great, and they outweigh the risks associated with chlorine.

    Chlorine is super-powerful stuff, which is why it’s so good at killing pathogens– but it has to be used correctly in order to be optimally effective… and when used appropriately, it’s not only safe but greatly beneficial. I just found this website that makes for a great resource for anyone determining whether a pool is safe:

  6. reddecember says:

    I was visiting family out in New Jersey this summer and they took me to their fancy fitness center. Their indoor pool was out of service because they were converting it to saline… basically salt water, was what I read.

    They were proclaiming the safety and bacteria killing abilities of this… and it surprised me. I’d like to learn more about just how safe this saline water is at keeping bacteria and pathogens at bay. There are a lot of pathogens which can live in high salt environments (halophiles). It’s an interesting concept though.

    • chem geek says:

      When people refer to a saline or saltwater pools they are almost always referring to a pool that has added salt (usually around 3000 ppm in the U.S.; 5000 ppm in Australia) along with a saltwater chlorine generator that converts chloride salt into chlorine. Such pools are obviously NOT chlorine-free, nor are they intended to be.

      The saltwater chlorine generator has the primary advantage of convenience since chlorine need not be manually added to the pool nor purchased and carried to other forms of automatic feed equipment (peristaltic pumps, etc.). The higher salt level in the pool is also closer to that of the eye (9000 ppm) so reduces osmotic pressure that can lead to discomfort. Some people like the feel of the higher salt levels.

      The downside is that the greater electrical conductivity can lead to faster rates of metal corrosion and higher chloride levels can be damaging to poorer grades of stainless steel. Splash-out of higher salt levels can harm softer stone surfaces.

  7. bad dog says:

    Great topic. A couple of summers ago, I went for a quick swim in a nice motel pool. In just a few minutes my eyes were super bloodshot and stinging. I mentioned it to the motel staff and they tested the pool water and immediately put up a ‘pool closed’ sign! One cannot assume pools are chemically ‘balanced’ and safe! What about the new ‘non-chlorine’ hot tub systems. Are there any independent studies showing they are safe?

  8. Terrance Morris says:

    Great point, bad dog. While chlorine is a great and effective chemical for cleaning swimming areas, it has to be used appropriately. They should have put that sign on the pool before you went for your swim– not after! As I said, I work with the American Chemistry Council, so I’ve seen a lot of studies. Here’s an article by Dr. Peggy Geimer that gets to the heart of some of the more recent questions about chlorine and pool safety:

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