Children swallow twice as much water as adults, and swimmers are more likely to ingest water in a pool than a natural body of water, according to a recent study by the US Environmental Protection Agency.

The study, published in the Journal of Water and Health, used cyanuric acid in urine as a measurement. Cyanuric acid passes through the body unmetabolized, making it easy to detect. The amount of cyanuric acid in the participants? urine allowed researchers to find out how much people consume.

Adults were found to swallow between 0 and 53 ml of water. Children under 18 swallowed from 0 to 154 ml, though 97 percent ingested 90 ml or less. The results are useful when assessing risks for recreational water illness transmissions, said Michael Beach, Ph.D., senior epidemiologist at the Centers for Disease Control and Prevention in Atlanta. For instance, a single ml of water can contain up to a trillion oocysts of cryptosporidium; the pathogen has been shown to cause infection and sickness with one to 100 oocysts.

Samples were taken from 53 participants who swam for 45 minutes at an outdoor pool disinfected with chloroisocyanate. Scientists collected urine for 24 hours, the amount of time it takes more than 98 percent of cyanuric acid to pass through the body.

The study also points out that swimmers tend to consider natural bodies of water dirtier and are therefore are more careful not to ingest water. Pool water, by contrast, was seen as clean.

Beach said if people are conscious about swallowing natural water for fear of contamination, he said, they should assume the same holds true in a pool.

?We have to do our best to educate people that it?s not drinking water,? he said.