Planning to hit an outdoor pool or waterpark this summer? You may want to think again. The average public pool contains nearly 20 gallons of urine, according to research from the University of Alberta, Edmonton. Swimming in strangers' urine is not only gross, it's also potentially dangerous. "Human urinary input into public swimming pools is a genuine health concern, although urine itself is sterile," the study explained. "Urine contains many nitrogenous compounds such as urea, ammonia, amino acids and creatinine. These compounds can react with disinfectants (chlorine) in swimming pools to form disinfectant byproducts (DPBs). Exposure to volatile DPBs...can lead to eye and respiratory irritation." Scientists took samples from 31 pools and hot tubs in two Canadian metropolitan areas and measured the amount of acesulframe potassium (ACE) found in each sample. ACE is an artificial substance used in foods like soft drinks and chewing gum. It's 200 times sweeter than sugar and unable to be broken down by the human digestive tract. ACE was present in 100 percent of the samples, even at levels that were 570 times higher than amounts present in standard tap water. Hot tubs were the worst offenders, with far higher urine levels than the surveyed pools. One hotel Jacuzzi contained more than three times the amount of ACE than the highest contaminated pool.