Warrick and Yates developed an approach to estimate the optimal seasonal water application for a crop based on soil water variability and salinity. This paper uses their approach to quantify the optimal irrigation amount for four cooperators from Central Arizona, accounting for irrigation water costs and crop value. The CVs of soil water across each cooperator's field varied by time of season and pre-vs-post irrigation, from 25% to 75%. Cooperator water management varied from overirrigation to underirrigation.