The water quality in rivers and streams and in selected aquifers in central Arizona basins in Arizona is described and illustrated. Major ions, nitrogen and other nutrients, and pesticides and some of their breakdown compounds were analyzed in both surface and ground water. Biological communities that included fish, invertebrates, and algae, were described in relation to stream water quality. Volatile organic compounds that originate from fuels, solvents, and industry were analyzed from ground-water samples. Agricultural and urban land-use effects on shallow ground water are compared and contrasted.