But that doesn't mean swimmers can't get sick this summer.

The new systems work by passing water through a chamber containing ultraviolet light bulbs, which sterilizes bacteria and parasites. But to be 99 percent effective, the water must be filtered three times. That will take up to 15 hours for large pools and three hours for kiddie pools. If a crypto-infected swimmer contaminates the pool before the water is treated, swimmers who swallow it can get sick.

Bottom line to protect your, ahem, bottom? Swim in the morning.

"This [UV system] will prevent a large outbreak, but it's not going to prevent people from getting crypto," said Jim Bossermen, the county's project manager over the UV system.

Ron Tobler, program manager over environmental health for the Utah County Health Department, worries the public will have a false sense of security when they enter a UV-treated pool. Pools in his county with the system had the same levels of crypto contamination last summer as regularly chlorinated ones, he said.

"There is no magic bullet out there. There's a part of me that is profoundly concerned about the UV systems that [are being] installed in Salt Lake as an answer" to eliminating crypto.

Still, UV is considered a better sterilizer than regular levels of chlorine. To be as effective as UV, chlorine levels would have to be raised from 2 milligrams per liter to 20. Such hyperchlorination was required last summer during the peak of the crypto outbreak and it required pools to be closed for eight hours.

On Thursday, the county showed off the UV system in West Jordan's Gene Fullmer Fitness and Recreation Center, the first pool in the county system to receive the technology. The county's remaining 17 pools should get theirs by the end of May. Several other public and private pool operators are adding the systems, too.

"I'll feel safe having my kids in the county pools," said Salt Lake County Mayor Peter Corroon, whose then-4-year-old son got crypto from a private pool last year.

Cathy Rappleye was teaching water aerobics at Gene Fullmer and is grateful for the UV system. She's in the pool every day. "In this pool there's lots of kids, so I'm a little worried."

Added 64-year-old swimmer Gerry Clements, "Exercising in the water is about the only thing I can do. . . . People should be able to use the county pools as much as possible."

The UV system will allow the county to use half the amount of chlorine, reducing the effects of the chemical, including so-called swimmer's asthma.

And it should cut down on the wear and tear on pool equipment. The county is replacing the pool slide at Gene Fullmer because the metal is eroding.

Utah logged 1,900 confirmed cases of crypto last year, though public health officials believe thousands more got sick.

hmay@sltrib.com