Source detection of low concentrations of Pb in water, for instance less than 15 μg L-1, may require a new methodology as the tolerances of Pb in drinking water are further reduced. It appears that the isotope properties of Pb may aid discrimination among natural sources and anthropogenic sources, including some plumbing materials. Characteristic Pb isotope signatures in a typical rural water supply district, located in Maine, are outlined. For example, unflushed drinking water lines have 207Pb/206Pb (0.850) and 208Pb/206Pb (2.130) signatures similar to Pb solders on pipes with ages of 7-38 years. Whereas reduced Pb concentrations in drinking water lines correlate with naturally distinctive signatures of 207Pb/206Pb (0.785) and 208Pb/206Pb (1.945).