In 1974 and 1975, experiments were conducted near Buckeye, Arizona to study the influence of municipal waste water on the growth and yield of cotton (Gossypium hirsutum L.). Two sources of irrigation water were used: (i) pump water from local wells (control treatment) and (ii) municipal waste water and pump water in a 50:50 mixture.Cotton irrigated with the waste water and pump water mixture grew taller with more vegetative growth than did cotton that was irrigated with pump water alone. When cotton was irrigated with the waste water and pump water mixture, the yields of seed cotton and lint cotton were higher than the yields from cotton irrigated with pump water. Cotton irrigated with waste water and pump water produced lint of the same quality as did cotton irrigated with only pump water.Municipal waste water can be used effectively as a source of irrigation water and plant nutrients in the commercial production of cotton in Arizona and, possibly, in similar environments throughout the world. When municipal waste water is mixed with pump water that is high in total soluble salts, the salt content of the mixture is lowered and the quality of the irrigation water in the study area is improved.