Chlorinated Pool Water Inactivates Coronavirus in 30 Seconds, Study Finds

Swimmers have wondered whether it’s safe to go back in the water over the past 13 months. A study released earlier this month should help them feel more comfortable.

Swim England, the governing body for swimming in the U.K., in collaboration with Water Babies, a baby swimming business, and the Royal Life Saving Society U.K., found that chlorinated water inactivates the coronavirus responsible for COVID-19 within 30 seconds.

“We performed these experiments at our high containment laboratories in London,” virologist and Imperial College London professor Wendy Barclay is quoted as saying in a news release. “Under these safe conditions, we are able to measure the ability of the virus to infect cells, which is the first step in its transmission.”

The study, which hasn’t been published in a peer-reviewed journal yet, established that “1.5mg per litre of free chlorine with a pH between 7 and 7.2 reduced the infectivity of the virus by more than 1000-fold within 30 seconds.”

In the U.S., the Centers for Disease Control and Prevention recommend that public pools and other treated swimming waters be carefully monitored so that the pH level—a measurement of how acidic or basic the water is—remains between 7.2 and 7.8. (These measurements are based on a scale of 1 to 14, with 1 being very acidic and 14 being very basic.) A reading of 7 is considered neutral, so the CDC recommends keeping pool water slightly on the basic, or alkaline, side of neutral.

The release reported that further “testing of different free chlorine and pH ranges confirmed that chlorine in swimming pool water was more effective with a lower pH— which is in line with current guidance for swimming pool operation.” This means pools at the bottom of the CDC's recommended pH levels would provide maximum protection against the coronavirus.

The study’s findings should come as welcome news to swimmers as pools across the country reopen and meets start back up as vaccinations become more widespread. The news, though, shouldn’t be surprising. Chlorine has been found to inactivate other coronaviruses and is effective at stopping other viruses, bacteria, and pathogens.

However, Swim England’s findings are the first of their kind amid the coronavirus pandemic and confirm what’s been said for months: The risk of transmission of the coronavirus via swimming pool water is very low.

Swimmers can still become infected with the coronavirus on a pool deck or in a locker room, meaning they should still adhere to social distancing guidelines and other safety precautions in those locations.

“These findings … add to the evidence that swimming pools can be safe and secure environments if appropriate measures are taken,” Swim England Chief Executive Jane Nickerson is quoted as saying in the news release. “The findings … will give everyone returning to the water peace of mind they are doing so safely.”