New Scientific Test Finds Up To 75 Liters of Urine In Public Pools (theguardian.com)

 75 Liters is just about 20 gallons of urine.

Scientists have developed a test designed to estimate how much urine has been covertly added to a large volume of water.

 "The test works by measuring the concentration of an artificial sweetener, acesulfame potassium (ACE), that is commonly found in processed food and passed through the body unaltered," reports The Guardian.

The findings are published in the American Chemical Society journal.

From the report: After tracking the levels of the sweetener in two public pools in Canada over a three-week period they calculated that swimmers had released 75 liters of urine -- enough to fill a medium-sized dustbin -- into a large pool (about 830,000 liters, one-third the size of an Olympic pool) and 30 liters into a second pool, around half the size of the first.

Although the researchers were unable to confirm exactly what fraction of visitors were choosing to quietly relieve themselves in the water rather than making the shivery trip to the changing rooms, the results suggest that the urine content was being topped up several times each day. 

The findings make for unwelcome reading, but swimmers might find some comfort in the measurements from eight hot tubs, which were found to have far higher urine levels. 

One hotel Jacuzzi had more than three times the concentration of sweetener than in the worst swimming pool. 

In total, the team sampled 31 different pools and tubs in two Canadian cities and found ACE to be present in 100% of the samples, with concentrations up to 570 times the background level in tap water samples. 

They used the average ACE concentration in Canadian urine to convert their measurements into approximate volumes of urine. 

Urine is not sterile.