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The story
A research team at the University of Alberta in Canada published a paper in 2017 that estimated how much urine gets mixed into swimming pools by measuring concentrations of the artificial sweetener acesulfame potassium. The findings sparked a wave of posts on 5ch sharing experiences and opinions about pool and bath etiquette and hygiene.
Published 8/26 (Wed) 6:05 AM
ITmedia NEWS
“Sweetened Swimming Pools and Hot Tubs,” a paper published in 2017 in the journal Environmental Science & Technology Letters by researchers at the University of Alberta in Canada, quantified the amount of urine mixed into swimming pools using artificial sweeteners.
Source: news.yahoo.co.jp / Read the original article here
What people said
Nah, the ocean's huge though.
That wasn't a pool, that was a potato-scrubbing tub. (Japanese slang for a spot so packed with bodies it looks like potatoes being scrubbed together in a barrel)
There are probably people out there who'll go their whole lives thinking that's what playing in water is.
there are surprisingly a lot of them.
Don't casually generalize your own messed-up daily habits to everyone else.
At outdoor pools, bugs are drowning all over the place anyway,
and at public pools you'll sometimes even see poop floating.
That's a joke, right? I hear this kind of thing a lot on 5ch, but
I want to believe people who actually pee in the pool are a tiny minority.
There are a lot of serious swimmers out there,
so probably about as much sweat pours in as from track-and-field athletes.
If anything, there's more sweat in there than urine.
Right?
Same goes for hot springs and spas.
After I've had a nice, satisfying pee, I watch the next guy come in and wash his face with the water and think, ugh, poor guy.
That's why I never take a spot downstream in the bath.
isn't actually from the chlorine, but from the pee?
Don't worry, it's true! 🤗
if you tested somewhere that isn't a natural hot spring, or a regular public bathhouse in Japan, the numbers would probably be way worse.
If it's a fresh-flowing natural spring source, no problem.
Even circulating baths filter the water, so the pee gets removed.
Never going back again.
That's like a phantom pregnancy or something lol
Before that, Downtown already spread it back when they were young hosts. (Downtown is a famous Japanese comedy duo)
Remember all those people who used to smugly lecture that washing your body before entering the bath is proper manners? They've all disappeared.
Guess they finally figured out that peeing after you get out is the objectively correct move.
Blindly trusting Japanese people's civility and good nature just makes you the fool.
It'd be hilarious if the ocean itself had a sign saying 'restroom here.'
Still, you should at least rinse off around your butt and privates before getting in.
I've actually seen someone with a piece of tissue stuck to their butt. Re: #83
Don't you mean Osaka, not Japan? (a jab implying Osaka's standards are on another level)
Astronauts purify and drink their own pee to save water in space. It's basically a perpetual motion machine.
Even natural spring water welling up from underground can be so contaminated near ranches that locals won't drink it, and water flowing through nature is often full of bugs, animal carcasses, and viruses — always boil it first.
Hmm, so is the ocean actually safer to swim in than the pool?
I've actually seen poop floating on the surface at a crowded beach, so who knows.
The total volume of seawater is like 500 trillion times the water in a 50-meter pool!!
Background and Key Points
The 2017 study, published in Environmental Science & Technology Letters by University of Alberta researchers, used acesulfame potassium (ACE) as a tracer. ACE is an artificial sweetener common in North American processed foods and drinks; the body doesn’t metabolize it, so it passes into urine unchanged and survives pool chlorination, making it a reliable marker for how much urine is diluted into a given volume of water — unlike most biological markers, which break down. The thread’s headline number, 571 times the concentration found in the tap water source (6–15 ng/L), describes contamination relative to the pool’s own fill water, not an absolute liter count, though the original Japanese framing (“how many liters of pee”) implied the latter.
The split in the thread wasn’t really about the science — almost nobody questioned the method. It was about behavior: several posters treated peeing in the pool as unremarkable, even routine, while others pushed back hard, insisting that can’t be normal and hoping the confessors were a minority. A side debate also broke out over whether the ocean is “safer” by dilution, versus the pool being a smaller, recirculated body.
What the thread leaves under-explained is the eye-irritation claim in >>32/>>62: red eyes after swimming aren’t caused by chlorine itself but by chloramines, formed when chlorine reacts with nitrogen compounds in urine and sweat — a detail the posters affirmed as trivia without explaining the mechanism. Also unaddressed: Japan’s own washing-before-bathing etiquette, cited sarcastically in the thread, exists specifically to reduce this same contamination in shared soaking water.
*This article is compiled from excerpts and a summary of the 5ch (Breaking News+) thread “[Study] How Many Liters of Urine Are Mixed Into a Pool? Measured Using Artificial Sweeteners — Canadian Team’s 2017 Study“.
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