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Chlorine: What Are Your Kids Swimming In?

It’s summer, and the kids are at day camp!

Unfortunately, for all the fun he’s having, my son has developed a rash, which my wife and I now suspect might have something to do with chlorine—after all, campers go to the pool twice a day, which is a lot of exposure to this all-but-ubiquitous water purification chemical.

Source: Dennis Wong on Flickr

It turns out that using chlorine to purify water has an interesting and controversial history that raises many questions about the price we pay for safety and public health.

Water was first purified with chlorine by the Scottish chemist William Cumberland Cruikshank in 1805. By the turn of the century, British chlorination of drinking water had sharply reduced deaths from Typhoid Fever.

In 1908, chlorine was added to drinking water in the U.S. for the first time in Chicago’s Union Stockyards. According to the American Chemistry Council [PDF],  the stockyard had been watering the animals from a stream “so polluted with meat waste that it bubbled with noxious gases,” and the animals were failing to thrive.

The stockyards were filtering the water, but it still contained high levels of dangerous bacteria, so they hired a New York water filtration expert, who added chlorine, “with the surprising result that the quality of the livestock drinking water was reported to surpass that of city water,” according to the Council.

In an even more interesting case, Jersey City was the first city to chlorinate municipal drinking water for human consumption in 1908, after a long legal battle between the city and its private water supplier. Dr. John Leal, an advisor to the water company, did research to show that water-born illnesses increased after flooding, which, he argued, indicated that water was contaminated from street runoff rather than at the source. As a solution, he proposed adding small amounts of chlorine to water and thereby started a trend that within a decade and a half had come to most American cities.

That these first examples are heralded by American Chemistry Council as heroic feats is in some ways ironic, because, by their own telling, chlorination was an end-use solution to comprehensive (and disgusting) design-flaws in the system: animals forced to drink from a river filled with meat waste, and municipal water that was routinely polluted with surface runoff.

Nonetheless, the widespread introduction of chlorine seems to have all but eliminated water-born illnesses in the developed world, though it is not certain to what degree better sanitation practices alone contributed, or if there are other solutions to achieve consistently clean, pathogen free water.

It’s an important question, because in spite of its apparent benefits, the widespread use of chlorine carries substantial risks as well. In higher concentrations, of course, chlorine is a potent poison, most notoriously used as a chemical weapon in the First World War, where it drifted across the landscape as a green cloud, sinking into trenches and eating away the soldiers’ lungs when they breathed it.

Source: Drake Goodman on Flickr
Source: Drake Goodman on Flickr

But even in very low does, there’s evidence that chlorine is not entirely benign. According to the United States Health and Services Toxicology program, chloroform, which can be found in the breakdown of chlorinated drinking and swimming pool water, is a known carcinogen. Epidemiological studies have suggested that the consumption of chlorinated water “may be associated with the development of certain cancers in humans.”

Other studies have linked swimming pool chlorine with elevated asthma, with the strongest correlation in young children – stronger than exposure to “all other factors combined” including tobacco smoke. Other sources have suggested that skin absorption of chlorine from hot showers is a serious risk to health. Ecological hazards are also well known.

Nearly two decades ago, the International Join Commission, an independent organization established by the U.S. and Canada to monitor and address water quality issues in the great lakes, issued a report advocating a complete phase out of chlorine and its by-products. And in 1994, President Bill Clinton asked the EPA to draw up a national strategy for “substituting, reducing or prohibiting the use of chlorine and chlorinated compounds” according to the New Scientist. As far as I can tell though, use of chlorine in drinking water and swimming pools is going on strong.

So, what’s the alternative? For drinking water, there are filters; if you’re concerned about showers, they can be installed at the house main, so that all domestic water use is chlorine free. Ozone disinfection is one time-tested alternative, but is potentially more complicated and more expensive than chlorine purification. Ultraviolet light has also been used, but (along with ozone) has been criticized for leaving no trace disinfectant in the water.

More radical is the idea of careful design and biological filtration. The fact that some 40 million Americans get their water from non-treated, private wells would seem to suggest that non-chlorinated water doesn’t automatically equal sickness and death.

Biological Filtration System at Oberlin College
Biological Filtration System at Oberlin College

In recent years, a number of companies and ecological designers have developed techniques to use artificial wetlands to purify water, and use of natural filtering systems in swimming pools is well established, at least in Europe.

So—chlorine has helped rid the developed world of serious diseases, but has created substantial risks of its own. Can we do better?

Natural Swimming Pool -- No Chlorine
Natural Swimming Pool — No Chlorine

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Mary Ostrowski
13 years ago

Chlorine in pool water destroys the germs that cause recreational water diseases (RWIs) like diarrhea, swimmers ear and skin infections. CDC stats show RWIs are on the rise and one cause of this disturbing trend is insufficient chlorine in public swimming pools. The rash your child developed after swimming could very well have appeared because there was not enough chlorine in the pool. For more information, and to bust a few pool myths, please check out

One hundred years after its debut in Jersey City drinking water, chlorine is used by the vast majority of water systems to help provide safe drinking water to families across America. In the years before chlorine’s introduction, waterborne diseases like cholera, typhoid fever, dysentery and hepatitis A claimed thousands of American lives every year. After a century of widespread use, germs that cause those and other serious illnesses have not developed a resistance to chlorine disinfection. Chlorine disinfection is critical to public health.

Mary Ostrowski
American Chemistry Council

13 years ago

Hi Mary,

Thanks for your response.

I have no doubt that chlorine kills germs! And no one wants to go back to an era of typhoid and cholera. But are those our only options? Either we treat our entire water supply treated with a hundred-year-old technology that is a known carcinogen or face epidemic disease? Don’t we have any other choices?

The answer is, we do. The fact that millions of Americans drink untreated well water without adverse effect would seem to be an indication that it is, in theory, possible to consume safe water without adding chemicals. And there are a number of water treatment alternatives.

As for swimming pools, not only do studies suggest that chlorinated pools increase the risk of asthma, but a 2008 study in Environmental Health magazine indicated that exposure to chlorinated pools by pregnant women as much as doubles the risk of certain birth defects.

Can you point me to any non-industry-sponsored studies to show that chlorine treated pools are safer than biologically filtered pools or any of the many other options now on the market, especially in light of the clear risks of chlorine?


Lakis Polycarpou

Renee Kashuba
Renee Kashuba
13 years ago


The website offered by Mary Ostrowski above, despite its healthy-sounding name, is an industry-sponsored website, presented by Water Quality and Health, which is sponsored by the Chlorine Chemistry Division of the American Chemistry Council: “It’s mission is to promote science based practices and policies to enhance water quality and health by advising industry, health professionals, policy makers and the public.” Further, it is a “body of independent scientific experts, health professionals and consumer advocates who serve as advisors to the Chlorine Chemistry Division of the American Chemical Council, an industry trade association. The WQHC assists in the interpretation of scientific information related to the various applications of chlorine disinfection, provides peer-review for Chlorine Chemistry Division of the American Chemistry Council documents, and advises the industry on its research priorities.” Members are paid honoraria and travel expenses to attend meetings.

In other words, Water Quality and Health was devised to research how to use chlorine, not how to avoid using it. Can we find someone from the Safe Water for Everyone Without the Use of Harsh Chemicals committee to comment?

13 years ago

Cool cool info. TKS all!

13 years ago

The natural filtration system is very interesting. I wonder if there would be a way to try it with a public pool. Since it’s natural, do you think people may be allergic? I know that people are allergic to chlorine, but perhaps a natural solution would encounter less problems.

13 years ago

The Richmond Plunge, a community pool in the Bay Area which has recently reopened has an ultraviolet purification system, as well as other green features.

Here is the link!


13 years ago

For 6 years I have used AquaSmarter in the pool of the house I avoid the chemicals and reduce the chlorine a 90% AquaSmarter helps me to eliminate the bacteria and virus by a system of low waterproof ionization cost and easy to use maintains to the water of the clean pool and of a healthy color. You can visit their webpage at: to obtain more information about this wonderful solution

13 years ago

I can assure you that the chlorine is the reason for a rash, not the lack of it. My in-law’s community pool is so chlorinated it burns your eyes and my daughter gets a rash every time we go there, so needless to say, we will be looking for another, more natural, place to swim.
Very interesting that it is 100 year old technology we are dealing with!
…And we wonder why cancer is on the rise…but we rely on chemicals as our only options. America is surely behind!

12 years ago

I agree with Michelle, the rash is probably the reason for the rash. We need to pay close attention to what our children are swimming in.

11 years ago

I found out via my own research my son has a chemical intolerance to ammonium chloride and has had serious asthmatic attacks that resulted in several trips to the emergency room after swimming. We need to find a better chemical to use other than chloride. These are our children, not pieces of rotten meat and garbage.

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