As summer approaches, many of us are looking ahead to languid days by the pool. New research, alas, suggests that many of them are laced with something other than water.

Though we all suspect it’s there, it’s not easy to assess how much urine there is in a particular swimming pool (the existence of a chemical that changes color when you pee is an urban legend). But it is not an insignificant public health question.

So a team of chemists at the University of Alberta in Canada has devised a new way to estimate the amount by measuring levels of an artificial sweetener commonly present in people’s urine.

The scientists sampled 29 pools and hot tubs in British Columbia and Alberta, and found the artificial sweetener, called acesulfame potassium, in every one.

In one residential, 110,000-gallon pool, they estimated the amount of urine to be nearly eight gallons, enough to fill the trash can you keep under the kitchen counter.

In a 220,000-gallon pool (one-third the size of an Olympic pool), the researchers estimated there were nearly 20 gallons of urine — roughly equivalent to the amount of water a standard washing machine uses per load.

Acesulfame potassium is often found in condiments, beverages, desserts, toothpaste and chewing gum. It’s an ideal proxy for urine, said Lindsay Blackstock, a graduate student who helped lead the study, because it passes through the body without being metabolized.

It is excreted exclusively in urine — unlike sucralose, shed mostly in feces. Other markers of urine, such as urea and potassium, are found in sweat as well as urine.

The components of urine and sweat — not to mention personal care products — react with chlorine to form compounds called disinfection byproducts that can irritate the eyes, lungs and skin. Pools owe their characteristic smell not to chlorine but to such a compound, trichloramine, which has been linked with asthma in professional swimmers and pool workers.

“I view these disinfection byproducts as roughly the equivalent of secondhand smoke — they’re things that just don’t have to be there,” said Ernest Blatchley, a professor of environmental engineering at Purdue University who was not involved in the new study.

Still, Blackstock stresses that overall the benefits of maintaining a healthy lifestyle through swimming far outweigh any potential risks from exposure to disinfection byproducts.

“The solution is simple,” she said. “Just be kind to your fellow swimmers.”