The Reservoir Storage Model (RSM) is a daily timestep water balance model for the simulation of reservoirs, lakes, ponds, tanks and wetlands. The model balances user defined inputs such as direct rainfall and pumped inflows, against losses such as evaporation, irrigation or water use demands, and environmental releases to simulate storage volume. The model includes functions for seepage losses, overflows, and substrate porosity to enable the simulation of wetland storage systems.