Ground water level measurements are very important for a wide range of applications in geosciences, agriculture, environment monitoring and mining industry. Currently, reliable and automatic ground water level measurements have not been realized. This paper presents the simulation and design of a segmented resistance sensor for measuring ground water level. Based on this sensor design, we have developed an instrument that can automatically log the ground water level. Finite element simulations were performed to optimize the sensor design and to gain insight into its response. Experimental results in the lab and field have verified the usefulness of the sensor.