The US Environmental Protection Agency (EPA) conducted a national survey to learn about the prevalence of 126 pesticides and pesticide degradates plus nitrates in public and private drinking water wells. This chapter describes the statistical design and chemical methods used in the survey. It presents estimates of contamination rates for public and domestic water supply wells. The chapter reports progress regarding the investigation of the relationship among contamination patterns, pesticide use, and ground water vulnerability. It discusses possible uses of the survey results in the Federal drinking water and pesticides programs. Six new multi-residue methods were developed for the survey, and two existing single residue methods were also used. Potential analytes were omitted from the methods if serious degradation during sample storage was demonstrated during analyte stability studies. The chapter discusses how EPA will use the results of the survey in its pesticide, ground water, drinking water, and non-point source water pollution programs.