The problem of controlling soil water within the root zone of irrigated crops to minimize the expected loss is examined. Control is obtained by the amount and timing of irrigations to replenish the soil water reservoir depleted by the crop's water consumption. Actual evapotranspiration rates are a function of the prevailing soil water level and the evaporative demand which may be considered to be either deterministic or probabilistic. For crops grown on a particular soil, an optimum soil water level is defined as the lowest soil water level above which crops are not stressed. The reduced yield of a crop is related to its growth stage and to the amount and duration that the soil water content is below this optimum value. Existing inventory models are adapted for the purpose of determining the optimal irrigation policy, that is, the timing and amount of water application that result in the maximum return to the irrigation farmer. Solutions to complex decision-making problems are currently available for a variety of irrigation situations. More realistic interpretations of the physical system are the claims made for using this new approach.