Water-quality data through 1979 in the Washita River basin within Oklahoma were examined for water type and suitability for public water supply and for irrigation use. Of 82 stations with available data, 32 stations or 39 percent were considered to have sufficient data for analysis. The classification of water type was based on the relation of the major ions: calcium, magnesium, sodium, carbonate, bicarbonate, sulfate, and chloride to each other within the range of measured specific conductance. The suitability for use as a public supply was based on the concentration distribution of selected constituents. The constituents selected were those with maximum contaminant levels established by regulation, or constituents for which recommended maximum limits have been established and for which historic data are available. The irrigation classification method of Wilcox was used to relate sodium, calcium, and magnesium concentrations and the salinity distribution to the suitability for use of the water for irrigation. Where data were available, the chance of phytotoxic effects by boron was discussed.