Keys to pool safety are vigilance and chemistry


When the weather gets hot, people seek relief. One of the nicest methods is by floating neck-deep in the sparkling blue water of a nearby pool.

But tally up the number of people likely to visit public pools each summer, and it may lead one to question how clean the water really is. Lots of people bring lots of bacteria into swimming pools, especially if they don’t shower before diving in. And bacteria can cause a variety of ailments — called recreational water illnesses — like diarrhea, norovirus, shigella or giardia.

Are public pools really clean?

Yes, thanks to chemistry and a little common sense, according to experts. Spending time in a favorite local pool is safe as long as it’s well maintained.

Ted Dowie is president of National Aquatics, the company that maintains Riverdale Neighborhood House’s pool. Its facility stays busy with patrons visiting every day of the week, which demands Dowie’s team diligently tests chlorine and pH levels hourly from dawn until the pool closes.

“Let me give you a tour of the basement,” Dowie said.

He slips into a room beneath the pool containing a mass of pipes, valves and heavy machinery. Water from the pool is pumped through three large holding tanks comprising the sand filtration system, which traps dirt and debris floating in the water.

Dowie’s company switched from liquid chlorine disinfectant to chemicals in pellet form. Those pellets, he said, are better for the environment and not as harmful to swimmers, but just as good at killing bacteria.

Filtration and proper chemical levels prevent a harmful overgrowth of bacteria. The right balance will prevent swimmers from getting sick if they accidentally swallow some water while not being so highly chlorinated that it burns swimmers’ eyes and respiratory systems.

In 2018, some 250 people were diagnosed with cryptosporidium, the most common and most concerning recreational water illness, according to Corinne Thompson, an epidemiologist in the waterborne illness diseases unit of the city’s health department. Chlorine kills most bacteria, but crypto can live, even in properly treated pools. It’s a parasite that causes watery diarrhea and stomach cramps.

“When a crypto case is reported to us, we reach out to the patient to interview them to understand where they spent time prior to getting sick,” Thompson said. Health officials deduce where the patient contracted the illness and may close down the facility until problems are resolved.

Thankfully, the health department rarely finds two or more patients who contracted crypto from the same pool, Thompson said. And while its numbers stayed low, more than 1,000 people last year were diagnosed with giardia, a diarrheal illness that’s spread through feces.

“That’s why it’s recommended that swimmers rinse off in the shower before entering the pool,” Thompson said, “because it removes a lot of dirt or anything else on the body.”

Health officials take action to avoid initial infection. Every pool, spa or steam room open to the public needs a city permit and regular health department inspections to operate, according to public health director Trevor McProud. The department also reviews all pool filtration system plans for new facilities to ensure sanitation.

“The health department’s really proud of its ability to inspect every facility every year,” McProud said. “We have a good compliance with the health code, and if we see violations that we consider a public health risk, we close the pool immediately until the issues are corrected.”

For an experienced pool technician like Dowie, safe water is a matter of keeping a detailed log of the water’s chemical profile so his staff can adjust chlorine levels accordingly.

“If the chemistry is off and you look into the water, you can’t see to the bottom,” Dowie said.

And a swimmer the lifeguard can’t see, he said, is a swimmer at risk.

The health department’s inspection records are open to the public, but Dowie recommends that any prospective swimmer who wants to ensure a pool is clean before taking a dip ask their chosen pool’s supervisor some simple questions about maintenance.

“The best questions would be to ask who their pool technicians are and what type of chemicals they use to treat the water,” Dowie said.

If bringing children who may be sensitive to a particular treatment method, ask if the staff uses liquid chlorine or dry chemicals for disinfection.

“Ask to see their daily readings, and from that you can tell if they’re keeping up with regular tests or if they’re faking it,” Dowie said.

“It’s very easy to ask, and they’re supposed to provide that when requested.”