Abstract: The Hamar geothermal field is one of many low-temperature geothermal fields in Northern Iceland. Since 1966 eleven wells have been drilled in the field. The purpose of modelling the behaviour of geothermal field under a variety of exploitation schemes is to obtain knowledge of the physical processes needed for further exploitation, control and management. On the basic data of observed water level, the physical behaviour of the Hamar geothermal field was simulated using a Lumped parameter mode1. Water level changes with varions production rates for the next 20 years are given. Conservative predicitous are obtained using dosed models, and optimistic from open models.