A new global study suggests that chlorination, a widely used method to disinfect drinking water, may increase the risk of certain cancers. Researchers found that people who drink chlorinated water face a 33% higher risk of bladder cancer and a 15% higher risk of colorectal cancer. This raises concerns about the long-term effects of chlorine in tap water.
The Risks of Chlorine in Drinking Water
For over a century, chlorination has been a cost-effective way to kill bacteria and viruses in drinking water. Since its introduction in the early 1900s, it has reduced deadly diseases like cholera and typhoid fever. This has helped increase life expectancy in many countries.
However, in the 1970s, scientists discovered that chlorine reacts with organic matter in water, such as plant debris, to create harmful byproducts. One of the most concerning byproducts is trihalomethanes (THMs). These chemicals include chloroform, bromoform, bromodichloromethane, and chlorodibromomethane. Studies on animals have shown that these substances can damage DNA and may cause cancer.
Are Current THM Limits Safe?
THMs are found in almost all public water supplies in the United States and the European Union. Regulatory agencies have set limits on THMs: 80 parts per billion (ppb) in the U.S. and 100 ppb in the EU.
However, the recent study suggests that cancer risks start at much lower levels. Researchers found that even 40 ppb, a concentration detected in New York City’s water supply, may increase cancer risk. The U.S. Environmental Protection Agency (EPA) reports that THM levels in most U.S. cities range between 40 and 60 ppb. Meanwhile, the Environmental Working Group (EWG), a nonprofit health advocacy group, recommends a much lower limit of just 0.15 ppb.
Large-Scale Study Links Chlorinated Water to Cancer
The new meta-analysis reviewed 30 studies and included data from 90,000 participants. This is one of the largest studies to examine the link between THMs and cancer. The results indicate that men face a higher risk than women, though scientists are still unsure why.
The study mainly focused on bladder and colorectal cancer because research on other cancers is limited. Experts believe that the bladder and intestines are at higher risk because these organs filter and process toxins in water.
The Challenge of Balancing Safety and Health Risks
These findings create a challenge for policymakers. Chlorination is necessary to prevent waterborne diseases, but it may also expose people to harmful byproducts. Water sources like lakes and rivers tend to have more organic material, leading to higher THM levels.
One possible solution is to filter organic matter from water before adding chlorine. This could reduce THM formation. However, reducing chlorine levels too much might allow dangerous bacteria to survive.
Lead researcher Emilie Helte, from the Karolinska Institutet in Sweden, warns that switching to alternative methods could be expensive and difficult to implement on a large scale. Some options, like ultraviolet (UV) light treatment and advanced filtration, reduce THMs but require significant investment.
How to Reduce THM Exposure at Home
Despite concerns about THMs, experts agree that tap water is still the safest and most regulated option for drinking water. Chlorination plays a key role in preventing deadly outbreaks of waterborne diseases.
For those who want to minimize exposure, one effective solution is using a granulated activated carbon (GAC) filter at home. These filters can remove most THMs and other contaminants.
Another method is allowing tap water to sit uncovered for a few hours before drinking. This allows some volatile chemicals, like chloroform, to evaporate. However, this method does not remove all harmful byproducts.
The Future of Water Treatment
While chlorination has saved countless lives, new research highlights potential health risks. Governments and water agencies must find safer alternatives that provide clean drinking water without increasing cancer risks.
Some experts suggest switching to a combination of filtration and alternative disinfectants, such as ozone treatment or hydrogen peroxide. However, these methods require further research to ensure they are effective and affordable for large populations.
As concerns grow about the long-term effects of chlorine byproducts, health organizations may need to reconsider current safety limits. Until then, consumers can take steps to reduce their exposure while still enjoying safe drinking water.
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