How Much Pee in a Pool is Too Much Pee?

Last week, a study by Chinese and American scientists revealed another reason to not pee in pools, which had more to do with chemistry than good manners.

The researchers found that when urine and chlorine meet in the right quantities, they can create two byproducts, trichloramine and cyanogen chloride. The latter can be harmful to the lungs, heart, and nervous system. It’s nothing to get your bathing suit in a bunch over, though. Even with chlorine levels far beyond what’s used in the average swimming pool, the amounts of these chemicals produced in the study were still in the World Health Organization’s “safe” range. In other words, you’re probably not going to hurt yourself emptying your bladder during a swim. That said, the study still warned that the chemical could “adversely affect air and water quality” in and around the pool. Plus, it’s just gross. 

At Ars Technica, the research made editor Casey Johnston wonder just how much pee in a pool it would take to make a harmful amount of those chemicals. And after some number crunching, Johnston found that creating a death pool of pee is a pretty tall order.

To get enough chlorine and uric acid together to create a toxic level of cyanogen chloride in an Olympic-sized swimming pool, Johnston says you’d need three million people emptying an entire day’s worth of highly concentrated urine into water that’s more chlorinated than normal.

“If you could get at that pool without dying of either suffocation or drowning in other people’s urine,” she writes, “you could probably pull off death by cyanogen chloride poisoning or at least a pretty good coma.”

Even in this pretty unrealistic situation, there’s a snag. Even at high concentrations, the researchers who did the study found that a lot of their chlorine was consumed by the uric acid. So really, you’d need an even higher chlorine concentration—a whopping half a liter of chlorine per liter of water—to create enough cyanogen chloride.

“In the end we need a pool that is two parts water to one part chlorine and would probably burn the eyeballs out of your sockets and make your skin peel away from your bones,” says Johnston. Get three million people to pee into that, without crushing each other or melting away like Nazis opening the Ark of the Covenant, and you’ve got enough cyanogen chloride to kill (also, the world’s worst pool party).

You can read Johnston’s whole thought experiment here.