Dissolved organic matter (DOM) in surface waters used for drinking purposes can vary markedly in character dependent on their sources within catchments. The character of DOM further influences the formation of disinfection by products when precursor DOM present in drinking water reacts with chlorine during disinfection. Here we report the development of models that describe the formation potential of trihalomethanes (THMFP) dependent on the character of DOM in waters from discrete catchments with specific land-use and soil textures. DOM was characterized based on UV absorbance at 254 nm, apparent molecular weight and relative abundances of protein-like and humic-like compounds. DOM character and Br concentration (up to 0.5 mg/L) were used as variables in models (R-2 > 0.93) of THMFP, which ranged from 19 to 649 mu g/L. Chloroform concentration (12 594 mu g/L.) and relative abundance (27 - 99%) were first modeled (R-2 > 0.85) and from these, the abundances of bromodichloromethane and chlorodibromomethane estimated using power and exponential functions, respectively (R-2 > 0.98). From these, the abundance of bromoform is calculated. The proposed model may be used in risk assessment of catchment factors on formation of trihalomethanes in drinking water, in context of treatment efficiency for removal of organic matter. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.