ABSTRACT
The water budget can be represented by using mass conservation equations. The simplest model represents a reservoir with water storage capacity S, inflow P, and flow losses Q and ET. The term P represents liquid and solid precipitation (rain, hail and snow) as well as occult precipitation caused by the condensation of water in the air (fog) and the phenomena of dew. Water resources or storage S is basically the groundwater, surface water, and water stored in the soil. The terms for the losses, Q and ET, represent runoff and the losses from evaporation and transpiration (evapotranspiration), respectively.
