HMTC Over 200 organic compounds have been tested for their reactivity with aqueous chlorine. Chlorine is the primary drinking water disinfectant in the United States. Four categories of reactivity have been established: (1) very reactive, all compounds reacting with chlorine with 90% or greater chlorine demand in 1 hour; (2) moderately reactive, compounds reacting to give a 90% chlorine demand in 1 week; and (3) nonreactive or very slightly reactive, compounds displaying little or no chlorine demand. Amino acids, phenolics, organic sulfur compounds, pyrroles, prolines, indoles, xanthines with amino group constituents, primary amines, some tertiary amine structures, secondary amines, and some purine compounds are classified as moderately reactive. Xanthines without amino group constituents, alcohols, nitroso, pyridines, aldehydes, ketones, carboxylic acids, ether structures, quinolines, amide structures, alkane and other straight chains, naphthalenes, and chlorinated hydrocarbons are slowly reactive to nonreactive. The compounds tested can serve as models for treatability problems. (21 ref.)