This article presents a method for analyzing the economic feasibility of modernizing irrigation systems. By using substitution relationships between two variables, one can determine irrigation performance and farm profit above which modernization would be justified from an economic point of view; and also the investments and energy consumption up to which modernization could be considered cost-effective. By means of representative average values, this method is applied to the now widespread conversion from surface irrigation to drip irrigation in Spain. Two conclusions are drawn. First, modernization may, in some instances, be justified only if more productive crop patterns are implemented. Second, saving water is a cheaper option than using an alternative resource only under certain conditions. [ABSTRACT FROM PUBLISHER]