State 1 of the Disinfectants/Disinfection Byproducts (D/DBP) Rule has recently lowered the maximum contaminant level (MCL) for total trihalomethanes (TTHM) to 80 ug/L and set an MCL for the sum of five haloacetic acids (HAA5) at 60 ug/L. Thus, regulatory and health concerns continue to highlight the need to minimize the production of halogenated DBPs. One approach is the removal of precursors, the natural organic matter (NOM). Colorado River water (CRW) is a low humic water in which the hydrophilic NOM has a strong influence. CRW NOM, including the hydrophilic NOM, was fractionated and isolated by techniques that minimize inorganic minerals contamination and allow structural characterization and chlorine reactivity evalution. Study of isolated hydrophilic NOM can provide needed insight into its nature and role in DBP formation and control. Two treatment schemes were studied: ozone/coagulation/biofiltration, and conventional ferric chloride coagulation/dual-media filtration. Five samples of CRW (plant influent, ozonator effluent, biofilter effluent, conventionally treated plant influent, and conventionally treated filter effluent) were collected, sodium-softened, and concentrated by reverse osmosis. The NOM was then isolated and separated into five fractions: hydrophobic (HPO), transphilic (TPI), hydrophilic acid plus neutral (HPIA+N), hydrophilic base (HPIB), and colloid fractions. Includes 20 references, tables, figures.