A study, administered over a three-year period by the Gulf South Research Institute under contract to USEPA, of commercially available home water treatment units was conducted to examine their effectiveness in reducing organics and the microbiological factors involved with their use. The discovery of extensive groundwater contamination demonstrated the need for information on the efficiencies of home treatment units in reducing volatile organic chemicals. The study was designed primarily to test most of the carbon units for trihalomethane (THM) reductions. These reductions were determined for 30 commercially available activated carbon units. Most water samples tested contained about 200 ug/L. The USEPA has established an interim standard of 100 ug/L for THMs. For the home treatment units tested, reductions of halogenated organics found in groundwater ranged from 55 to 99 percent. The surface water test paralleled that for groundwater, with the addition of 3 chemicals: p-dichlorobenzene, hexachlorobenzene, and chlordane. The validity of these latter findings are dubious, due to the use of hexane-methanol. With respect to the testing of other units, data are considered sufficiently valid to indicate potential treatment capabilities under the test conditions for the two reverse osmosis units, the ozonator, and the ultraviolet-activated carbon unit. Includes 6 references, tables, figure.