Haloacetic acids or HAAs are carboxylic acids in which one or more halogen atoms take the place of hydrogen atoms in the methyl group of acetic acid. In a monohaloacetic acid, a single halogen replaces a hydrogen atom: for example, in bromoacetic acid. Further substitution of hydrogen atoms with halogens can occur, as in dichloroacetic acid and trichloroacetic acid.
Haloacetic acids are a common contaminant in treated drinking water, particularly water subjected to chlorination.