Effects of Chlorine in Water: What You Need to Know

Chlorine is an abundant, naturally-occurring element that has been used to disinfect water for more than a century. Since chlorine is used in thousands of municipalities to disinfect water, the assumption has long been that it is safe for human consumption and exposure. Yet, researchers and scientists have warned about the potentially dangerous effects of chlorine for decades—specifically, the effects of chlorination by-products, also called disinfection byproducts (DBPs).1,2

We’ll explore what chlorine is and how it’s used today, how chlorine can interact with other elements to create hazardous by-products linked to cancer, and what consumers can do to reduce their exposure to chlorine through the use of water filtration systems and other measures.

Effects of Chlorine in Water

Chlorine: From the Battlefield to the Swimming Pool

Chlorine is a chemical element in the halogen group (symbol CI on the periodic table) found in the Earth’s crust. It exists as a gas in its natural state, although it’s rarely found in this form—most chlorine is found in the form of ionic chloride compounds, which includes table salt.

Chlorine is used directly and indirectly in the manufacture of a surprising number of products, including:


·         Dyes ·         Paints
·         Foods ·         Paper products
·         Household items ·         Plastics and other petroleum products
·         Insecticides ·         Solvents
·         Medicines ·         Textiles


Most people come into direct contact with chlorine from their tap water, swimming pools, and medications.

Chlorine - From the Battlefield to the Swimming Pool

Chlorine gas was used as a chemical warfare agent in World War I—the toxic chemical would severely burn the lungs and body tissues of enemy soldiers, often killing them. Even small doses of chlorine by everyday people can cause physical symptoms. If you’ve ever experienced chest tightening, coughing, watery eyes, or wheezing after inhaling chlorine vapors in low doses, you can imagine what acute exposure of a large amount of this toxic substance can do to the body.


Chlorination By-Products (AKA “Toxic Trash”) in Our Water Supply

Chlorine is used to kill bacteria and harmful pathogens in our drinking water supplies. As a  chemical disinfectant, chlorine has played an important role in reducing infections from pathogens like cholera and salmonella; that doesn’t mean that long-term exposure to even low doses of chlorine in our water supply is necessarily safe, however. Let’s explore.

While chlorine may be relatively harmless in low doses, when it interacts with organic matter (such as fallen leaves, soil, and even sewage and livestock manure) problems can emerge in the form of chlorination by-products. These by-products have been the subject of much scrutiny by the scientific community over the years, as they may increase cancer risk.

The amount of chlorination by-products found in any given water source depends on two primary factors:

  • The amount of chlorine added to the water
  • The amount of organic matter present in the water

A family of chlorination by-products called trihalomethanes is particularly dangerous. The Environmental Protection Agency (EPA) calls them “disinfection by-products,” while the Environmental Working Group (EWG), a consumer protection organization, had a less flattering name for them: toxic trash.3

The EPA regulates four members of the trihalomethane family:

  • Chloroform, an anesthetic with the power to knock people out cold
  • Bromodichloromethane
  • Bromoform
  • Dibromochloromethane

In its 2013 report, Water Treatment Contaminants, Forgotten Toxics in American Water, the EWG notes that chloroform has been deemed a “probable” human carcinogen by the U.S. government. Officials in the state of California consider chloroform a “known” carcinogen.

Other trihalomethanes (including the ones listed above) found in drinking water supplies are thought to cause thousands of cases of bladder cancer every year. They have also been linked to colon and rectal cancer, low birth weight, miscarriage, and birth defects.4,5


How Extensive Is the Problem of Chlorination By-Products?

The EWG analyzed water quality tests conducted in 2011 that were made public by 201 municipal water systems in 43 states across the U.S. Each one of the tests revealed trihalomethane contamination. To put this into perspective, it means that more than 100 million Americans were exposed to these toxic by-products in 2011. This exposure continues today.  Chlorination By-Products in Our Water Supply

While nearly all of the municipalities tested showed trihalomethane levels below the limit of 80 parts per billion set by the EPA in 1998, the Environmental Working Group points out that this limit may be too high to be considered safe, pointing to mounting evidence since 1998 showing the dangers of trihalomethanes at lower levels.

This includes data from studies in France, Spain, and Finland showing that men exposed to more than 50 parts per billion had a significantly increased risk of bladder cancer. A scientific team in Spain also found that exposure to trihalomethanes at greater than 35 parts per billion increased bladder cancer risks.


Trihalomethanes “Just the Tip of the Iceberg”

The EWG further cites studies showing more than 600 unwanted chemicals created by the interaction of disinfectants used to treat water and pollutants in the water—most of which have not received much study.

Among these are haloacetonitriles, haloaldehydes, haloketones, halohydroxyfuranones, haloquinones, and aldehydes, some of which are suspected carcinogens.

Exposure to a group of by-products called haloacetic acids during the second and third trimesters of pregnancy may be linked to intrauterine growth retardation and low birth weight; this is based on evidence of carcinogenicity in animals, according to the EWG report.


Exposure to Chlorine While Showering and Swimming

Particularly troubling is that up to two-thirds of our everyday exposure to chlorine and its by-products happens during showering, through inhalation of steam as well as skin absorption.6,7

Exposure to Chlorine While Showering and SwimmingWarm and hot showers open up the pores of the skin, allowing for increased absorption of chlorine and other chemicals that lurk in our water. Steam from a shower concentrates chemicals at as much as 50 times the level of tap water—this is because many chemicals, including chlorine, vaporize at a lower temperature and much faster than water.

Shower vapors contain chlorine gas—chloroform—which, as we mentioned earlier, is a “probable” carcinogen according to the U.S. government.

Chlorine vapors can irritate sensitive tissues inside our bodies and out—it is for this very reason that it was used as a chemical weapon during wartime. Chlorine exposure is bad for our lungs, and it’s damaging to our skin and hair, robbing them of moisture and elasticity, which can negatively affect our appearance over time.

It’s clear that chlorine should be avoided as much as possible. So, what can you do to protect you and your family from exposure to chlorine and its toxic by-products? Let’s explore.


Eliminating Chlorine in Water to Reduce Your Exposure

Here’s the good news: Chlorine is one of the easiest products to remove from water with a carbon filter. Here are some steps to take:

  • Invest in a water purification system for your whole home. An experienced water expert that specializes in water filtration can evaluate your needs and make recommendations for your particular situation.
  • Carry bottled water with you while you’re out, rather than relying on municipal water supplies (from drinking fountains, taps, etc.). You can fill your bottles at home before you leave or keep a supply of bottled water on hand.
  • Avoid using chlorine in your pool, if you have one. Use natural products whenever possible. A pool cleaning company can consult with you on which natural products to use.
  • Use water filters in sinks and bathtubs.
  • Cleanse your body immediately with organic/all-natural soaps after exposure to chlorine. Use the EWG’s Skin Deep database to search for cleansing products that don’t contain harmful chemicals.

By taking these and other steps, you can dramatically reduce your exposure to chlorine and its by-products—and the health of your family and you are well worth it.

Eliminating Chlorine in Water to Reduce Your Exposure



  1. http://www.cdc.gov/safewater/chlorination-byproducts.html
  2. http://science.sciencemag.org/content/331/6013/42.summary
  3. http://www.ewg.org/research/water-treatment-contaminants
  4. http://www.scientificamerican.com/article/earth-talks-tapped-out/
  5. http://www.globalhealingcenter.com/natural-health/chlorine-cancer-and-heart-disease/
  6. http://www.bioray.com/content/Chlorine.pdf