Chlorine is commonly used to disinfect drinking water. When it is added to water that contains organic matter such as runoff from farms or lawns, however, it can form compounds such as chloroform that can cause illness.

The study by the Environmental Work Group and Public Interest Research Groups identified ares that may have increased health risks including miscarriage, neural tube defects and reduced fetal growth from women drinking chlorination byproducts. ...

...  The environmental groups combed water-quality records in 29 states and the District of Columbia and matched them with various research into birth defects and miscarriages.