The occurrence of metals, such as lead and copper, in household drinking supplies can often be a result of the corrosion of pipes and joints in water distribution systems. One measure of the potential for water to cause corrosion is the Langelier Saturation Index (LSI) (Langelier, 1936). The LSI is a measure of the potential for water to deposit a mineral layer (scale) within a water distribution system that can inhibit the corrosion of pipes and joints. Negative values of LSI suggest mineral deposition is not likely to occur while positive values indicate conditions favorable to mineral deposition. Negative values of LSI might be indicative of conditions that lead to elevated concentrations of metals, such as lead and cooper, in household water. The LSI was computed for groundwater samples from 20,962 locations in the United States. The data for the computations of LSI were obtained from the US Geological Survey (USGS) National Water Information System (NWIS). The data included in this report are for groundwater samples obtained during the period 1991-2015. At each location, the most recent sample (during the period 1991-2015) with the necessary measurements was used to compute the LSI. For the purposes of assessment (Langland and Dugas, 1996), LSI values less than -0.5 were classified as potentially corrosive; LSI values between -0.5 and 0.5 were classified as indeterminate; and LSI values greater than 0.5 were classified as scale-forming. Of the 20,962 sites, 31.5% were classified as potentially corrosive, 63 % were classified as indeterminate, and 5.4% as scale-forming. The values of LSI presented in this report can be used to identify which areas in the U.S. might be more susceptible to elevated concentrations of metals, such as lead and copper, in household drinking water and which areas may be less susceptible.