Haloacetic acids are byproducts formed when chlorine disinfectants react with organic matter in water. This group of 9 compounds is regulated due to potential cancer risks.

Haloacetic acids (HAA9) are a group of nine chemical compounds that form when chlorine-based disinfectants react with naturally occurring organic matter in water. These byproducts can continue to form in distribution systems after treatment. The EPA regulates HAA9 levels, typically measured in parts per billion (ppb). Water utilities can reduce HAA9 formation by removing organic matter before disinfection or using alternative disinfection methods. Ongoing research aims to better understand their long-term health effects.