A recent meta-analysis of 30 studies involving 90,000 participants found that water chlorination levels common in the US and EU likely increase bladder cancer risk by 33% and colorectal cancer risk by 15%.
Chlorine reacts with organic matter to form trihalomethanes (THM), toxic byproducts present in nearly all public water systems.
Although chlorine disinfection has reduced waterborne diseases, these findings pose regulatory challenges.
Alternatives exist but are costly. Experts recommend continued tap water use with effective filtration, such as granulated activated carbon.