London-based experts studied how chlorinated pool water affects SARS-CoV-2
They concluded the risk of transmission during swimming is 'incredibly' low.
Chlorinated swimming pool water can inactivate the virus that causes COVID-19 in just 30 seconds, a study found as indoor pools re-open across England this week.
Virologists from Imperial College London studied the impact of varying concentrations of chlorine in water on the SARS-CoV-2 virus.
The findings suggest that the risk of COVID-19 transmission via swimming pool water is 'incredibly' low, the researchers reported.
The investigation was commissioned by Swim England and the Water Babies swim school, with support from the Royal Life Saving Society.
'We performed these experiments at our high containment laboratories in London,' explained study author Wendy Barclay, of the Imperial College London.
'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.
'By mixing the virus with swimming pool water that was delivered to us by the Water Babies team, we could show that the virus does not survive in swimming pool water — it was no longer infectious.
'That, coupled with the huge dilution factor of virus that might find its way into a swimming pool from an infected person, suggests the chance of contracting COVID-19 from swimming pool water is negligible.'
In the study, Professor Barclay and colleagues found that a concentration of free chlorine of 1.5 milligrams per litre and a pH of between 7–7.2 reduced the infectivity of the SARS-CoV-2 more than 1,000 fold within just 30 seconds.
Further tests using different chlorine concentrations and pH levels concluded that the chlorine in swimming pool waster is more effective with a low pH level.
This, the team said, is inline with current guidance for swimming pool operation — which recommends a free chlorine concentration of 1.5 milligrams per litre and a pH level of 7.0.
'These findings suggest the risk of transmission from swimming pool water is low,' said Swim England chief executive Jane Nickerson.
The study, she continued, 'adds to the evidence that swimming pools can be safe and secure environments if appropriate measures are taken.
'It’s fantastic news for the operators, our members and clubs who take part in all our amazing sports, recreational swimmers and those who rely on the water to stay physically active.
'The findings confirm the guidance we have issued to operators is correct and will give everyone returning to the water from Monday [April 12] peace of mind that they are doing so safely.'
'We are excited about these findings as we prepare to restart our classes and plan to welcome back families, littles ones and customers to indoor swimming pools across the country,' said Water Babies founder Paul Thompson.
'It has been fantastic to work closely with Professor Barclay and her team at Imperial College and collaborate with leading bodies Swim England and RLSS on this world-leading research.'