The most common method for keeping swimming pools free of microbial pathogens is to add chlorine. Unfortunately, the chlorine in the water can combine with other molecules to form harmful byproducts like trichloramine (NCl3) and cyanogen chloride (CNCl). Researchers from China Agricultural University and from Purdue University found that this is particularly apt to happen when the chlorine is combined with uric acid.
Now, before you jump to conclusions, I should say that uric acid is present in human sweat. In really tiny amounts. There’s nearly 400 times more uric acid in urine than in sweat. So, I guess go ahead and jump to that conclusion because according to the authors, about 93% of the uric acid in swimming pools comes from pee.
How bad could it be? Well, NCl3 has been associated with severe lung injury. CNCl can affect the heart, lungs and central nervous system.
Bottom line: don’t pee in the pool. Even if you’re an olympic swimmer.