Maybe you'd prefer not to think about it, but people do use a dip in the local swimming pool as an opportunity to relieve themselves. But in the grand scheme of things, how much pee are we talking about here? Scientists in Canada have conducted a study aimed at attaching some figures to this unsavory conundrum, and while the results do resemble drop-in-the-ocean-type proportions, they'll still be enough to make you a little more suspicious of those swimming nearby.

Researchers at the University of Alberta (UA) were able to measure the quantity of urine in public pools by searching for traces of a telltale artificial sweetener. Known as acesulfame potassium or ACE for short, the sweetener is widely consumed through processed foods and things like diet soda. It's good for those drinking diet sodas because it is not absorbed into the body and therefore doesn't add calories, and by the same token, it is good for scientists studying urine in pools because it passes right on through.

The research team began by taking samples from 29 public pools in two Canadian cities and indeed found elevated levels of ACE. It then tried to better understand the ratios at play by using the method to track urine levels in two public pools across three weeks, one with a 830,000 liter (220,000 gal) capacity and the other with a 420,000 liter (111,000 gal) capacity.

Over the three-week period, the team estimates that swimmers leaked 75 liters (20 gal) of body waste into the larger pool and 30 liters (8 gal) into the smaller pool. One way of looking at this is that the urine amounted to around 0.009 and 0.007 percent of the total pool water, respectively. Another way of looking at it is that 75 liters is like somebody filling up a small bathtub with urine and pouring it into the pool. Do with that information what you will.

The scientists say that they can't use the data to get a handle on how widespread this activity is, for that they'd need to know how many people used the pool and how much each culprit is releasing at a time. They do note, however, that while urine is largely sterile on its own, in a swimming pool the nitrogen-containing components such as ammonia and urea can react with disinfectants to create more harmful products, such as trichloramine, which is a lung and eye irritant and has also been linked to asthma. The risk, therefore, may be understated.

"We wanted to focus on urine because when there is a fecal incident at a swimming pool, everybody knows about it," says UA PhD student Lindsay Blackstock. "The pool has to be evacuated and then shocked. On the other hand, urination in a pool really goes unnoticed and a lot of people might be doing it."

With that said, the researchers do emphasize that the health benefits of swimming for exercise and recreation far outweigh the risks. Please just stop by the restroom before you dive in.

The research was published in the journal Environmental Science & Technology Letters.