A lumped-parameter, linear-reservoir, ground-water model is developed for possible application to the Mesilla Valley, New Mexico. Using a discretized form of the model, specific-yield and response-time parameters are estimated by a least squares technique from water-level and drain-flow data for the Mesilla Valley. Net recharge is then estimated from water-level changes during months that recharge occurs. The estimated parameters are used in simulations which predict water levels and drain flows. The results show that the parameters are physically realizable and similar to values used by others. The simulations are in excellent agreement with the observed data over a five-year period.