Scientists know that you pee in the pool | Science News for Students

Scientists know that you pee in the pool

Researchers can now measure the urine people leave in swimming pools and hot tubs
Apr 26, 2017 — 12:00 pm EST
pool urine

A new technique measures an artificial sweetener in pools to estimate how much pee swimmers have left behind.


We know you would never do it. But some people pee in swimming pools and hot tubs. This isn’t just a gross habit. When chlorine reacts with urine, it creates chemicals that can irritate eyes and lungs. Now researchers can measure this disgusting behavior. They’ve found a simple way to estimate the volume of urine in a pool.

The technique could help people decide when to change some or all of the water in a pool or hot tub, the researchers say. But the new research isn’t really meant to create new rules for pool managers. It’s supposed to emphasize a message: Don’t pee in the pool!

By itself, urine in pools isn’t a problem. That’s because a healthy person’s pee is typically sterile, or germ-free, says Lindsay Blackstock. She’s an analytical chemist at the University of Alberta in Edmonton, Canada. But pool water also contains chlorine, a chemical that kills germs. Trouble can arise when that chlorine reacts with urine. It can trigger the production of dozens of new byproducts. Many of these new chemicals will cause no harm. But some, especially one called trichloramine (Try-KLOR-ah-meen), are known irritants.

pool sign
If recent tests are any clue, a lot of people ignore signs like this one.
tano_d’ere/Flickr (CC-BY-SA 2.0)

Even if you’ve never heard of trichloramine, you’ve probably smelled it. That distinct “swimming pool smell” at most pools doesn’t come from the chlorine, notes Blackstock. It’s trichloramine. It can sting the eyes. The pungent chemical also can irritate the lungs.

As pee in a pool increases, the amounts of trichloramine will too. The more trichloramine there is, the more irritating it can be to swimmers. So Blackstock and her teammates wanted to see if they could estimate how much urine was present in pool water. There’s no simple way to test for urine directly. (Have you ever heard that pool water has a chemical in it that will change color if you pee? That’s only a myth.)

So the researchers needed a marker for the urine — some other substance that would signal the likely presence of pee. And that’s what caused them to focus on acesulfame (ASS-eh-sul-faym) potassium. It’s an artificial sweetener used in foods and drinks. It’s sold under the brand names Sunett and Sweet One. The chemical is also called Ace-K for short.

It makes a good marker for pee, says Blackstock. For one, it has no natural sources and is very stable. It doesn’t break down at normal temperatures, which is why many food manufacturers use Ace-K. Even after being stored in foods at room temperature for 10 years, it won’t have broken down. It also won’t break down in pools or be removed during water-cleanup treatments.

Moreover, Ace-K passes right through the human body without being digested. That makes it a great choice as a low-calorie sweetener (the body doesn’t get any energy from it). But it also made Ace-K a good choice for their study, says Blackstock. The substance doesn’t leave the body in sweat, breath or poop. Ace-K only leaves the body in urine. And when it comes out, it will be the same form of the chemical as had been ingested.

Foul findings

First, the researchers needed to know how much Ace-K is present in the average person’s urine. They collected urine samples from 20 people and mixed them together. Each milliliter of urine (about one-fifth of a teaspoon) contained about 2.36 micrograms of Ace-K.

Then, on 15 days in August 2016, the team collected water samples from two swimming pools in a city in Canada. One pool held about 420,000 liters (110,000 gallons). The other had about twice that volume. On the same days, the researchers also collected three samples from the city’s water supply.

Liter-sized samples of the city’s tap water contained between 12 and 20 nanograms of Ace-K. (Remember, Ace-K doesn’t decompose during water treatment.) If there were no pee in the pools, they should have had similar levels of Ace-K. The smaller pool, though, had 156 nanograms of Ace-K per liter of water. And the larger pool had even more, about 210 nanograms per liter. That adds up to about 30 liters (almost 8 gallons) of urine in the small pool. The larger pool held a whopping 75 liters (almost 20 gallons) of pee!

These pools probably aren’t unusual, says Blackstock. In 2014, the same researchers found Ace-K in unusually high concentrations in 21 public swimming pools, 8 hot tubs and even a private swimming pool. In other words, every pool and hot tub they tested had pee in it. Blackstock and her team shared their new findings online March 1 in Environmental Science & Technology Letters.

The team’s approach “is a pretty cool idea,” says Beate Escher. She’s a toxicologist at the Helmholtz Center for Environmental Research in Leipzig, Germany. Researchers have used Ace-K before to measure water pollution, she says, both on and just beneath Earth’s surface. And Ace-K holds some advantages over other substances, such as caffeine, that researchers have used as a marker of urine. Caffeine, for instance, can break down after it leaves the body. “Ace-K is much more stable,” Escher says.

Like Blackstock and her team, Escher suggests the best way to tackle urine is pools is prevention, not clean-up. So please, she urges, don’t pee in the pool: “Self-control is the best thing.”


Power Words

(more about Power Words)

analytical chemistry     A field that focuses on ways to separate materials into their parts or elements. A scientist in this field is an analytical chemist.

artificial sweetener     A chemical substance that has a sweet taste but few or no calories. People and food manufacturers add artificial sweeteners to foods and drinks to give them a sweeter taste. Many different artificial sweeteners exist. They include saccharin, sucralose and aspartame, among others.

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

behavior     The way a person or other organism acts towards others, or conducts itself.

caffeine     A natural, plant-based stimulant, which activates the nervous system and heart. The leaves, seeds and fruits of many plants contain caffeine. In coffee plants and tea bushes, caffeine acts as a natural pesticide.

calorie     The amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. It is typically used as a measurement of the energy contained in some defined amount of food.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical can also be used as an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemical reaction     A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).

chlorine     A chemical element with the scientific symbol Cl. It is sometimes used to kill germs in water. Compounds that contain chlorine are called chlorides.

concentration     (in chemistry) A measurement of how much of one substance has been dissolved into another.

disinfect     To clean an area by killing dangerous infectious organisms, such as disease-causing bacteria.

environmental science     The study of ecosystems to help identify environmental problems and possible solutions. Environmental science can bring together many fields including physics, chemistry, biology and oceanography to understand how ecosystems function and how humans can coexist with them in harmony. People who work in this field are known as environmental scientists.

germ     Any one-celled microorganism, such as a bacterium, fungal species or virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

marker     (in biomedicine) The presence of some substance that usually can only be present because it signals some disease, pollutant or event (such as the attachment of some stain or molecular flag). As such, this substance will serve as a sign — or marker — of that related thing.

online     (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.

potassium     A chemical element that occurs as a soft, silver-colored metal. Highly reactive, it burns on contact with air or water with a violet flame. It is found not only in ocean water (including as part of sea salt) but also in many minerals.

sterile     An adjective that means devoid of life — or at least of germs. (in biology) An organism that is physically unable to reproduce.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.


Journal:​ ​​L.K.J. Blackstock et al. “Sweetened swimming pools and hot tubs.” Environmental Science & Technology Letters. Published online March 1, 2017. doi: 10.1021/acs.estlett.7b00043.