When we drink a glass of water, we ingest an unknown amount of by-products that are formed in the treatment process. And we don't know what many of them are. However using advanced technology, researchers at Linköping University have been able to detect new compounds -- where every water treatment plant has a unique combination.

Swedish water treatment plants work hard to ensure the high quality of our drinking water. In order to prevent the spread of diseases, the plants must chlorinate the water. But chlorination can lead to the formation of by-products that can be hazardous to our health.

Normally, tests are conducted for a small number of known by-products in our drinking water, including trihalomethanes (such as chloroform), which are regulated by the Swedish National Food Agency. Now a collaboration between researchers at Linköping University (LiU) and various water treatment plants has resulted in new advances in the hunt for by-products in drinking water.

"Using advanced technologies we've been able to trace more compounds, which were detected at the molecular level. It turned out that most of the by-products were unique to each water treatment plant. This means that specific conditions at each plant affect which by-products are formed," says Anna Andersson, doctoral student at LiU's TEMA M -- Environmental Change.

For one year Anna Andersson has worked closely with four Swedish water treatment plants, where each has different raw water and treatment processes, taking samples of the water. The results showed that even at the plants where no traces of the regulated trihalomethanes were detected, a wide range of other by-products was present.

The researchers were also able to detect a large variation of by-products at the plants that use chloramine, a milder form of chlorination, in the treatment process.

Chlorination important to prevent spread of disease

The large variation of by-products makes it difficult to know how to best reduce the health risks of these compounds.

"Sometimes people talk about the cocktail effect, and that's what we're faced with here. What we have to understand is how we can reduce the risk of the entire mixture of compounds. The risks of the individual by-products that have been identified are unknown, but the potential risk of the cocktail is reason enough to try to reduce the formation of by-products," says Anna Andersson.

Chlorination is one of our most important defences against bacteria in drinking water, and it plays an important role in ensuring good water quality throughout the supply network. The researchers are trying to discover how to continue to use chlorination effectively, while reducing the exposure of unwanted by-products.