A stand alone ultrasonic ranging system (SAURS) was designed and applied in hydrological measurements of water levels in rivers, lakes and water reservoirs. Water level ranging is carried out through air by an electrostatic ultrasonic transducer which is controlled by a microprocessor based system. The data is collected in a 64 kByte EPROM cassette. The problems associated with temperature correction were studied theoretically and experimentally. The results suggest that the main temperature effect is related to the temperature dependence of sound velocity in air. It was found that a precision of 1 cm at a distance of 600 cm can be readily obtained provided that air temperature is measured to within 1 degrees C. Level measurements carried out by the SAURS were found to be in excellent agreement with measurement made by a mechanical float-type water level recorder. The advantages of remote water level measurement, as compared to direct contact methods, is examined and discussed.