Drinking water: how to deliver it chlorine-free?

If you have spent time in southern Europe or overseas, you are probably familiar with the taste of chlorinated tap water. Distributing tap water with residual chlorine is a century-old strategy used to protect populations by preventing the proliferation of waterborne pathogens. But is it necessary? In a commentary published in the journal Science, researcher Urs von Gunten from EPFL and his colleagues at Eawag provide evidence from Europe showing that chlorine could be forgone if other protective barriers are in place.

Three factors determine the quality of tap water: the quality of its source, of its treatment, and of its distribution network. Decades of experience in the Netherlands, Germany, Austria, and Switzerland have shown that, when none of these three elements are compromised, the number of waterborne-disease outbreaks are low, even lower than in countries that add chemical disinfectants to their water supply in order to compensate for poorly maintained networks, insufficient water treatment, or contaminated water sources.

But the researchers point out that distributing the water without added chlorine comes at a cost. It requires protecting groundwater sources, properly controlled water treatment, and regular maintenance of the water distribution network. But where chlorine can be foregone, the benefits go beyond improving the taste of tap water. When disinfectants, like chlorine, react with natural organic matter that is always present in drinking water, this can lead to the formation of disinfection by-products, some of which are potential carcinogens.

The article was authored by researchers from EPFL, the Swiss Federal Institute of Aquatic Science and Technology (Eawag), Michigan State University, University of Iowa, University of Colorado and the University of Sheffield.