Despite the importance of irrigated pecan (Carya illinoinensis) production in arid and semi-arid regions of the U.S. and Mexico and the reliance of successful production on adequate and optimal management of water, the detailed water balance for irrigated pecan production is poorly understood compared to other important horticultural and agronomic crops. Our goal in this review is to summarize what is known about the water balance of irrigated pecans with an emphasis on flood irrigation (the most common irrigation method) and to identify research needs to improve our understanding of the water balance and how to better manage water for this very profitable and productive crop. We consider the following components of the water balance: 1) evapotranspiration (ET), 2) evaporation from the soil surface (E), 3) water stored in the soil profile (S), and 4) deep percolation (DP). ET represents the largest component of the water balance, comprising 60-90% of the water applied, depending on application methods and management. DP beyond the root zone represents the largest non-plant use component and depending on its original source and fate, can contribute to net groundwater recharge if from surface water, return flow if pumped originally from the groundwater, surface water return flow if moved horizontally and discharged to a stream or drain, or a net loss if moved horizontally and consumed by non-target plants. E represents a consumptive loss that reduces water use efficiency with respect to pecan production, though it can provide some cooling benefits in the orchard. It is generally a small, but not insignificant, quantity of the applied water (5-10%). There is considerable room for improving water use through alternative irrigation methods and/or improved water management.