What's Living in Your Hot Tub?

From the WebMD Archives

May 26, 2000 (Los Angeles) -- With summer just around the corner, your thoughts are probably turning to lazy days on the beach, getting some sun, and perhaps a nice twilight soak in the hot tub before barbecuing for dinner. But without proper disinfection of that hot tub, germs could multiply and ruin your summer overnight.

Organisms found in hot tubs can cause a wide variety of ailments, including skin rashes and infections, urinary tract infections, irritation of the digestive system, and even hepatitis and Legionnaires' disease. As long as you maintain your tub properly, there's little danger of catching something.

Bromine is the disinfectant most commonly used in hot tubs, and chlorine is also used, but in recent years manufacturers have developed a number of disinfecting systems that don't use either chemical. However, scientists at the University of Arizona in Tucson studied several of these systems and found that if you don't follow the instructions to the letter, germs can proliferate to dangerous levels. They presented their findings at a microbiology meeting here this week.

Lead author Pamela Watt, MS, and her colleagues conducted the study in two parts. In the first part, they used a "simulated" spa one-twelfth the size of an average real-life spa They compared the disinfecting abilities of bromine or ozone added to the tub's circulation system to enzyme or bromine tablets added to the water directly. They heated the water first, added the disinfectant, and then added two kinds of bacteria associated with skin infections or fecal contamination. After 30 minutes, the investigators took water samples to measure bacterial growth, or lack thereof. Bromine and chlorine were both effective at holding down bacterial growth, with bromine added to the generating system having a slight edge after 30 minutes. Neither ozone alone nor the enzyme had much of an effect.

In the second phase of the study, Watt and her colleagues tested disinfecting systems in real hot tubs under real-life conditions: two people sitting in the tub for 30 minutes at least four times in one week. This time they compared a generated ozone system to a silver ion cartridge and a silver ion cartridge with a chemical known as MPS added. In that portion of the study, only the silver ion cartridge plus MPS was better than ozone at discouraging bacterial growth.


"Basically the take-home message is, if you are going to use ozone in your spa, you must use chlorine or bromine also," says Watt, a research specialist in the department of soil, water, and environmental science at the University of Arizona. To be effective, she says, there must be a residue of disinfectant in the water at all times. "Ozone is a wonderful disinfectant, but it does not maintain a residual level," she tells WebMD. It simply does not last long enough in the water or on the surface of the tub to have an ongoing effect.

"If you buy a system [with instructions to add something] you have to add it," she says. "If you want to maintain a spa with clean water, make sure you follow the instructions. Consumers need to be wary of chlorine-free products and they need to [add these chemicals] every day. If you skip even one day you could have [a problem]." Swimming pools present less of a risk because the colder water is less inviting to bacterial growth.

"As long as you can smell the bromine in the water, you're OK," says microbiologist Jon J. Calomiris, PhD. Calomiris was not involved in these studies but conducted his own studies of bromine disinfectants in hot tubs while a graduate student at Johns Hopkins University in Baltimore. He recommends adding bromine in a concentration of five milligrams per liter of water in the tub and warns consumers to heat the water before adding the chemical, as disinfection works better at higher temperatures. He tells WebMD that there are no known side effects of bromine in these amounts and that it is, in fact, less irritating than chlorine.

If you use someone else's spa, both Watt and Calomiris warn against standing around in your bathing suit afterward. That gives any bacteria trapped between you and your suit even more of an opportunity to come into contact with your skin. "The next day you'll have a rash that looks like the bathing suit," says Calomiris. Watt recommends getting out of your suit as soon as possible and bathing after using the spa.


Vital Information:

  • Without proper disinfection, germs can grow in hot tubs and cause skin rashes, infections, digestive problems, and even hepatitis and Legionnaires' disease.
  • Researchers note when using ozone for disinfection, chlorine or bromine also should be used, because they linger in the water and help prevent germ growth between cleanings.
  • A researcher adds that heating the water and using five milligrams of bromine per liter of water are effective methods of controlling germs. Hot tubbers also should change out of their wet bathing suits quickly so germs don't have extra time against the skin to cause problems.
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