It takes a lot of chemicals to make pool water safe for swimming.
Untreated water can accumulate harmful Escherichia coli and Salmonella bacteria and protozoans such as Cryptosporidium parvum and Giardia lamblia. So, the disinfection chemicals are necessary for killing pathogens, but at the same time, they don’t just float around inertly in the water: Many of them react with organic material in the water—dirt, sweat, urine, and even skin moisturizers—to form Disinfection By-Products (DBPs).
The water in pools must be disinfected to make it safe for swimming. But the disinfectants added to pools aren’t just killing harmful microbes. They’re also reacting with organic/inorganic matter in the water brought in the water by swimmers themselves. Anybody who goes to a pool is going to be exposed to these DBPs—in the water or in the air around it. Some building blocks for making DBPs are introduced from the tap water that’s used to fill the pool. But most of them are brought along for the ride from people using the pool. Some DBP precursors are on the skin: hair, skin cells, dirt, or personal care products. Others are in sweat or urine. Actually, urine contains a lot of urea, a nitrogen-laden molecule that reacts with chlorine in pool water to form a DBP called trichloramine. This resultant chemical—not the chlorine itself—helps gives indoor pools or any public pool their distinctive “chlorine” odor. “Of the volatile DBPs formed in swimming pools, trichloramine is usually cited as the most volatile and has been linked to various adverse human health effects,” Blatchley says ( Ernest R. (Chip) Blatchley III is an environmental engineer at Purdue University who studies water treatment and DBPs.)
Olympic swimmers have admitted to routinely peeing in the pool since they have long practices.
So, the more you exercise and the harder you breathe, the more DBPs you’re likely to take up. And the more people that pee in the pool, the more likely it is for there to be high DBP levels.
Professional swimmers are the most likely to be affected by DBPs, both because of the amount of time they spend around pools and because of their propensity to pee in the pool. They’re also the ones who are best positioned to do something about it.
The most common compounds used to disinfect swimming pools are forms of chlorine.
Other disinfectants include bromine, ozone, and ultraviolet radiation. They all kill microbes by reacting with and disrupting the function of biomolecules the organisms need for survival. The various disinfectants can be used alone or in combination.
Combinations of disinfectants might be needed because some pathogens are resistant to chlorine.
Cryptosporidium—a protozoan that goes by the nickname “crypto” and causes intestinal disease—is more often than not the microbe that causes illness in recreational swimmers, says Ernest R. (Chip) Blatchley III, an environmental engineer at Purdue University who studies water treatment and DBPs. Crypto is resistant to chlorine but sensitive to UV radiation, which doesn’t kill the protozoan but makes it unable to reproduce. The radiation source must be hidden away inside the water recirculation and filtration system
“If you couple UV and chlorine together, you have a strategy that can take care of virtually any microbial pathogen that might be present in pools,” Blatchley says.