How Much Pee Is In This Pool? Chemistry Has Answers, If You Dare

Do you pee in the pool?  Maybe it’s a habit you outgrew, but for every potty-trained graduate of age-group swimming there are a dozen more older and “mature” swimmers that would still rather just let it go than get out during practice. After all, most swimmers only ever get out of the pool to pee right before the hard set–we see you, slackers, but we’re not debating the actual sizes of your bladders here.  In fact, we applaud your willingness to walk all the way to the toilet, because as Dr. Xing-Fang Li from the University of Alberta has discovered, your teammates that stay put haven’t stopped answering nature’s call in your shared aquatic field of play, the pool.

So, do you still want to know how much pee is in a pool?  Well, assuming you’re swimming in a standard eight-lane, 25 yard pool, which holds approximately 220,000 gallons of water, you’re also swimming in about 20 gallons of urine. Your best friend’s backyard pool, which likely measures around 20 feet long by 40 feet wide at about five feet deep, probably contains “only” two gallons of pee.  In either case, this translates to approximately 1/100th of 1% of the pool’s total volume.  Peanuts, right?  Well, it turns out it’s not that simple.

Even a volume as tiny as 1/100th of 1% of the pool’s volume can be a hazard to patrons’ health.  How?  Well, when urine and chlorine bond in their objectionable union a whole host of unsavory compounds known as disinfection byproducts are born.  Such byproducts include the chloramines floating in the air that swimmers and pool-goers breathe in, giving pools that classic chlorine odor, to cyanogen chloride, a chemical so dangerous it is classified among chemical warfare agents, to nitrosamines, substances which are usually carcinogenic.  While there’s not enough evidence to say whether the nitrosamine levels in pools increase risk of cancer, one Spanish study found a trend in bladder cancers in some long-term swimmers.  Apparently, even peeing in the pool can generate bad karma that might bite you back in the very organ you sneakily relieved during that social kick your coach was nice enough to pencil into the workout.

So how did scientists determine these volumes in the first place?  Well, if it leaves your body, it had to find its way in somehow, so in the case of pee, scientists followed the Yellow Brick Road back to artificial sweeteners which leave a distinct and traceable residue in pool water.  For this study, Dr. Xing-Fang Li measured the amounts of acesulfame potassium, or Ace-K for short, in competition pools, hotel pools, and hotel hot tubs in two Canadian cities.  University of Purdue’s Dr. Ernest Blatchley III equated peeing in the pool to second-hand smoke, saying that the habit is “disrespectful and potentially dangerous.”  However, as Blatchley points out, any pool open for wide-spread or public use is definitely absorbing its fill of urine.  Essentially, pee in the pool is a foregone conclusion–even a joke among many swimmers–so best prepare to deal with it.

Any swimmer or swim parent can tell you how much worse air quality tends to be in natatoriums than at outdoor pools.  Without open air and sunlight, airborne compounds like chloramines build up and are more concentrated, making breathing more difficult, especially for those with respiratory issues such as asthma.  What’s more, urine isn’t the only unpleasant substance finding its way into common waters via the human body.  Oils on the skin and in the hair, and products used on the body such as lotions and hair gels, all contribute to the sump that pool water can become if both patrons and aquatics directors and staff do not take the necessary precautions to side-step inadvertently adulterating the seemingly pristine waters within which we swim.

Thankfully, the path to a cleaner pool is simple.  First, if you gotta go, just get out of the pool and go, or go before practice, or hold it. Your choice!  Second, actually take a shower before getting in the water like the sign in the locker room says.  It might seem redundant to shower before getting in the pool, but by rinsing off whatever residue is on your skin and hair before getting in the water, you’re doing everyone in the pool, on deck, and in the stands a favor.  So there you have it–there really is a lot of pee in the pool, but with any luck, we’ll keep a few gallons out!

The original study this information is drawn from can be found here.  For further scientific reading about chloride formation in swimming pools and other disinfection byproducts, click here.

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in competition pools, hotel pools, and hotel hot tubs …..I suspect its a lot higher in hotel pools, and hotel hot tubs


I for one, am more likely to pee during practice, because I don’t want to miss a set. You don’t miss anything if you get out of a hotel pool to pee


Don’t let Phelps see this!! Otherwise he will never want to come back.


And I naively believed that pools contain “urine-indicator dye” to detect if anyone is peeing in the water. Only after reading this article I actually looked it up in the internet… Sigh, no such compound. I wonder why – would it be too difficult to create?

About Reid Carlson

Reid Carlson

Reid Carlson originally hails from Clay Center, Kansas, where he began swimming at age six.  At age 14 he began swimming club year-round and later with his high school team, making state all four years.  He was fortunate enough to draw the attention of Kalamazoo College where he went on to …

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