A common disinfectant in drinking water breaks down into a chemical compound we know almost nothing about, including whether it has any potential toxic health effects to those who drink it.

Chlorine has been used to sanitise drinking water for more than a century. However, some drinking water systems in the US, UK and Australia now use a closely related chemical disinfectant called chloramine. That is because chlorine byproducts were linked to bladder and colon cancer, low birth rates and miscarriage, says Julian…