PHOENIX -- Swimming pools across the Valley opened for the summer on Memorial Day weekend, but how clean is the water?

A new study by the Water Quality and Health Council found that nearly one in five adults admits to urinating in a swimming pool instead of using the toilet.

Eight in 10 adults are convinced their fellow swimmers are guilty of such a crime, the study said.

Nevertheless, health officials insist that swimming in and even swallowing urine-contaminated water isn't harmful to someone's health.

"Urine in itself has been purified through a whole variety of bodily processes so that it's removed a lot of the contaminants in it," said Don Herrington from the Arizona Health Department.

Swimmers should be more concerned about swallowing parasites than swallowing urine, officials said.

Last summer, dozens of swimmers got sick from pool water, forcing the closure of all 29 Phoenix city pools; the parasite which caused the illnesses, Cryptosporidium, comes from diarrhea.

Phoenix Parks and Recreation spokeswoman Amy Blakeney urged sick swimmers to stay out of the pool.

"People who are sick need to stay home and remain at home for 14 days after they're symptom-free, especially if they have diarrhea," Blakeney said.

Though city pools electronically monitor chlorine levels, the city of Phoenix has begun to require swimmers to shower before they jump in the pool as an extra precaution.

"Taking a shower allows those materials to rinse off and go down as sewage, and then gets a clean body into the pool water, which is what we all want," Blakeney said.