With the recent at-the-tap monitoring under the Lead and Copper Rule by approximately 7700 large and medium-sized US public water suppliers between January 1992 and December 1993, and with the treatment adjustments being implemented by some of these suppliers, a new opportunity now exists for examining what measures are likely to significantly reduce residential tapwater lead and copper levels. Thus, a primary purpose of this research is to begin to harness this emerging body of data and experience to determine through rigorous statistics analysis what water quality characteristics and/or treatment modifications can be expected to statistically reduce residential lead and copper levels and to what extent. This research utilized two distinctive methodologies which are combined to develop a better understanding of tapwater lead dynamics and to provide public water suppliers a clearer picture of the effectiveness of various options for reducing 90th percentile lead levels. The first methodology involves recruitment of volunteers from across the US from all ages of homes and plumbing system types to have their water tested for lead in exchange for providing information about their residence. The second methodology involved an extensive survey of US public water supplies for their finished water quality and treatment methods followed by a statistical correlation of these data with the 90th percentile lead levels observed for their systems during the first two rounds of monitoring under the Lead and Copper Rule.