Scientists have now identified an easy way to measure pool urine—by looking for traces of a common artificial sweetener. Urine in pools mixed with chemicals can pose a potential health threat.
Certain sweeteners are designed to go right through you and don’t break down readily in pool water, which means it can be isolated and measured. Scientists have calculated that one 220,000-gallon, commercial-size swimming pool contained almost 20 gallons of urine.
That .01 percent can still cause health problems
Source: The Strong Smell Of Pool Chlorine Is Actually Urine Plus Chlorine : Shots – Health News : NPR