Provides information on (1) what is known about the quality of drinking water from community water systems & private wells in six states -- California, Illinois, Nebraska, New Hampshire, North Carolina, & Wisconsin -- & (2) what factors influence the quality of drinking water from these sources. Contains a recommendation designed to help ensure that owners of private wells are better informed of potential contamination problems whenever groundwater-based community systems detect contamination that may also be present at nearby private wells. Charts & tables.