Chemical found in US drinking water is linked to 15% higher risk of colorectal cancer, 33% for bladder cancer

Here’s more evidence that your drinking water may be unsafe.

A new analysis out of Sweden reports that disinfecting water with chlorine creates chemical byproducts that can increase the risk of bladder cancer by 33% and colorectal cancer by 15%.

The culprit appears to be trihalomethanes (THMs), which are made up of four compounds — chloroform, bromodichloromethane, dibromochloromethane and bromoform. THMs are found in nearly all public water systems in the US and European Union.

“What we see is alarming and we need some more high quality studies,” lead study author Emilie Helte, a researcher at the Karolinska Institute in Sweden, told the Guardian. 

The US has treated drinking water with chlorine for over a century. Routine disinfection began in 1908 in Jersey City, NJ.

The practice was so successful at eradicating waterborne illnesses, such as cholera and typhoid fever, that it quickly got adopted by the rest of the country and has been a public health staple since. 

But, by the 1970s, scientists discovered that adding chlorine to water also brings downsides in the form of potentially harmful byproducts like THMs and haloacetic acids (HAAs). 

The Environmental Working Group (EWG) has long warned that THMs and HAAs may increase the risk of cancer and reproductive issues.

Men may be at greater risk than women, according to the new research, published last month in the journal Environmental Health Perspectives.

The analysis, a review of 30 scientific studies involving over 90,000 participants, found elevated cancer risks with THM levels as low as 40 parts per billion (ppb).

THMs have been detected at 38.1 ppb in NYC’s water supply, according to EWG data from 2013-19.

The US limits THM in drinking water to 80 ppb, while the EWG recommends not exceeding 0.15 ppb.

Helte notes that this problem doesn’t have an easy solution. “It’s really important not to use too little disinfectant,” she said, and installing new filtration systems to remove harmful toxins would be costly. 

For now, she advises people to continue drinking tap water and recommends using granular activated carbon to filter harmful chemicals at home.

Helte’s research follows recent reports about “forever chemicals” in US drinking water supplies. One study linked these manmade chemicals to a 33% higher incidence of certain cancers.