The SPAW (Soil-Plant-Air-Water) model simulates the daily hydrologic water budgets of agricultural landscapes with two connected modules, one for farm fields and one for impoundments such as wetland ponds, lagoons or reservoirs. The model was developed to understand and predict agricultural hydrology and its interactions with soils and crop production. It can be adapted to a wide variety of hydrologic analyses including: Estimation of runoff and seepage from agricultural fields and design and performance evaluation of agricultural ponds, lagoons and reservoirs for water supply, waste management and water management. Simulation results estimate a daily vertical water budget depth of all major hydrologic processes including runoff, infiltration, evapotranspiration, soil water profiles and percolation. The SPAW model is free, but users must register to download and install the program.