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Covid-19 and swimming: The scientific factors you should know

"I don't see the risk really coming from the water itself."

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While temperatures heat up and summer sets in, people will be looking for ways to cool off. As swimming facilities consider reopening and swimmers ponder a dip, it’s worth understanding how swimming influences your risk of catching or spreading Covid-19.

The short answer? Swimming itself, in a pool or body of natural water, doesn’t appear to pose any extra risks virus-wise. But that doesn’t mean pool parties get the green light, scientists caution.

Ernest Blatchley is an environmental engineer at Purdue University who studies how disinfectants in swimming pools react with contaminants and pathogens.

"In a well-operated pool, the water itself should present minimal risk and probably an acceptable risk for most people," Blatchley tells Inverse.

"But the risks for disease transmission in a pool setting are not zero because we don't spend all our time underwater."

Swimmers might become infected with Covid-19 from a viral droplet from a strangers' sneeze, or by touching surfaces in the changing room or shower. Research shows the Covid-19 virus can survive for up to 72 hours on plastic and stainless steel surfaces, which may include a pool ladder, deck chair, or door handle.

"There's nothing about a pool that would eliminate the need for social distancing, avoiding contaminated surfaces, or not breathing air from somebody who's close by," Blatchley says.

Can the Covid-19 virus live in water?

According to the Centers for Disease Control, there is “no evidence” that the virus that causes COVID-19 can be spread to people through the water in pools, hot tubs, spas, or water play areas.

That's because chlorine and other common disinfectants, like bromine, ozone, or UV sanitizers, likely kill SARS-CoV-2 in treated water. Chlorine is thought to disarm microorganisms in as little as 30 minutes.

Charles Gerba is a microbiologist and virologist at the University of Arizona who studies how viruses survive in water. He tells Inverse that chlorine does "an excellent job of killing bacteria and viruses — even viruses that are more difficult to kill than coronaviruses like SAR-CoV-2."

But while chlorine is a potent and popular disinfectant, how the chemical actually deactivates viruses isn't well understood.

It's theorized that chlorine damages viral proteins and nucleic acids, which can keep the virus from infecting a host cell and inhibits their reproduction — effectively rendering them harmless, Blatchley explains.

UV light — from UV pool sanitizers or the sun — also damages bacteria and virus's nuclear material. It's often used in tandem with chlorine to wipe out microorganisms in water. Exposure to sunlight may generally make surfaces around outdoor pools less risky virus-wise compared to indoor pools, Blatchley says.

"But that's going to be different in North Dakota than it's going to be in Miami," he says. "And it's going to be different on a cloudy day than on a sunny day."

Currently, there's no data exploring how common water disinfectants affect the Covid-19 virus specifically, Blatchley says. But data on other viruses with similar structure suggests SARS-CoV-2 would be killed by these disinfectants.

"There's nothing about this virus that I know of that would prevent it from being effectively inactivated by these conventional disinfectants that we use," Blatchley explains. That is, unless there's something "really weird," like a possible resistance to disinfectants in certain parts of the virus.

It's possible that the virus may be more sensitive to chlorine and other common water disinfectants than other viruses because it has an envelope structure. Enveloped viruses tend to be sort of "wimpy viruses," Blatchley says. They're relatively fragile, sensitive to physical or chemical stress, and tend to be inactivated quickly by disinfectants.

Saltwater pools are also likely to be low-risk, because pool equipment called salt cells use electrolysis to generate chlorine from salt in the water. Meanwhile, swimming in a river, lake, or ocean is unlikely to be radically different risk-wise to pool water.

"Viruses which infect humans usually survive less in seawater than freshwater — so seawater contamination would be seen as a lower risk," Gerba says.

Some of these venues might also be safer as they tend to be less crowded.

"I don't see the risk really coming from the water itself," Blatchley says. "It's really the things that surround the water that present the risk."

If you're in a crowded area, you have increased your risk of becoming infected, Blatchley says.

"It doesn't matter that you happen to be standing in water or standing at the mall," he points out. "It's really that air that you're breathing that other people are affecting."

Is it safe to swim? — Ultimately, the decision to swim or not to swim is a personal one that depends on a range of factors: if facilities are open, how crowded they may be, and the potential mental and physical benefits of the activity.

If you do decide to jump in, there are key precautions advised by public health authorities: practice social distancing, avoid potentially contaminated surfaces and practice good hand hygiene. This means washing your hands, using hand sanitizer, and avoiding touching your face.

Gerba also says showering before going into the pool would be a good idea.

"As long as the pool is chlorinated and people practice safe distancing, I think pools are okay," Gerba says.

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