IRA FLATOW: Now, it’s time to play good thing, bad thing.

Because every story has a flip side. As you know, it’s been unseasonably warm this week. Maybe it’s got you thinking about summer pool season, taking a dip. Well, you might want to think twice about putting a toe in the water or the rest of your body because thanks to a study published this week we now have an idea of just how much of that pool water is actually urine.

Yeah. That’s what I said. How did researchers discover this? Well, you could say it was a pretty sweet bit of chemistry. Lindsay Blackstock, PhD student at the University of Alberta in Edmonton. Welcome to Science Friday.

LINDSAY BLACKSTOCK: Hi. Thank you so much for having me on your show.

IRA FLATOW: How could there be good news on this?

LINDSAY BLACKSTOCK: Well, I suppose the good news is that we’re able to take this opportunity of this really intense media attention we’ve gotten to promote public health and good swimming hygiene practices because we don’t want people to be afraid of swimming. That’s for sure.

IRA FLATOW: Well, tell us how this all came about? How do you keep track of how much pee is in the pool?

LINDSAY BLACKSTOCK: Absolutely. So first of all, we’re not actually measuring urine. We’re measuring an artificial sweetener called acesulfame. And acesulfame is unique because it is consumed quite widely among the general public because it’s present in a lot of different processed foods and drinks. And it’s also very stable so it moves through your body very quickly and it’s not metabolized. So it exits the same way that it goes in.

And what’s unique about acesulfame is it’s excreted 99% in urine. So if we’re finding it in swimming pools and hot tubs that the only logical explanation we can come up with why it’s at elevated levels is because people have to be peeing in the pools.

IRA FLATOW: Wow. And do you think this is on the low side? Because if somebody is peeing in the pool and hasn’t taken some artificial sweetener in the past 24 hours they’ll be missed, won’t they?

LINDSAY BLACKSTOCK: Sure. So we always have to keep in mind all the sources of error that can go into these estimations that we make. So the way that we came up with the estimation is we looked at 20 Canadian urine samples, mixed them all together, and got the average that way for how much Ace or acesulfame was in Canadian urine. So absolutely.

When we did that calculation we were doing it based on the average sweetener we found in Canadian urine. That assumption could be wrong. There could be people who are urinating in the pools that haven’t had any of that artificial sweetener. And there could be ones that maybe they’re eating a lot of sweetener and they’re not urinating. So there’s a lot of factors that can play into that.

IRA FLATOW: So how much pee is in the pool?

LINDSAY BLACKSTOCK: And again, so what we estimated was the volume of urine that would be required to lead to the concentration of acesulfame in the pool. So we found in one larger size pool, about one third the size of an Olympic size swimming pool, was 75 liters of urine. And then one half that, which was about 110,000 gallons, was 30 liters of urine. But keep in mind that doesn’t mean that 30 liters of urine is present because urine can be very difficult to measure in swimming pools and hot tubs because it’s broken down quite quickly.

IRA FLATOW: So is there any way for me or a layperson to measure that ourselves with a home test kit?

LINDSAY BLACKSTOCK: Not at this point. No. But most university chemistry departments or chemistry labs should have the analytical instrumentation to do this type of test. And that’s why we proposed it as a strategy to potentially monitor urine input into swimming pools.

IRA FLATOW: So what’s to be gained by this study instead of just informing us? Is there any good stuff to come out?

LINDSAY BLACKSTOCK: Well, really what we want to tell the general public is that we really want to promote swimming. We think it’s a great form of exercise. We also want to make sure that we acknowledge all the pool operators and facility operators because they do a wonderful job.

IRA FLATOW: But the bottom line is don’t pee in the pool.

LINDSAY BLACKSTOCK: Exactly. Don’t pee in the pool. We don’t want to scare people. We don’t want to stop disinfecting pools because it’s a great way to make sure we don’t–

IRA FLATOW: We’ve got to go.

LINDSAY BLACKSTOCK: Oh, sorry.

IRA FLATOW: That’s OK. Thank you for joining us, Lindsay Blackstock, PhD student at the University of Alberta.

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