Criteria based on economics are essential to rationalize water use from the highest investment payback perspective in irrigated agricultural systems decision support. The central goal of this work is to provide theoretical basis for calculating the optimal time of water supply in freedrainage furrow irrigation systems. The purposed methodology might be generalized to different situations, being basically explained by: a) yield function (total applied water versus yield); b) duration of each phenological stages followed by their corresponding crop coefficients; c) parameters regarding to advance and infiltration equations; and d) information related to price of marketable products, costs of water and the other production factors. The specific values of parameters and attributes should be provided or suggested from users. The outputs to be achieved should denote a time of water supply regarding to maximum mean net income, which is obtained from different scenarios of water deficits that are corresponding to different fractions of required water to be infiltrated at the end of the furrow.