During several investigations of ground water contamination, relatively large fluctuations in ground water levels—which occurred in a time interval shorter than that necessary to collect a round of water levels—were observed. However, because of their short-term nature, it was not possible to collect the data necessary to characterize fully the effects of these fluctuations when using standard water level measurement techniques. Without such a characterization, these short-term fluctuations in ground water levels can seriously impair interpretation of the ground water flow system. In a case history presented, tidal and other environmental influences were large enough to make a normal round of water level data useless in interpreting ground water flow. Monitoring of water levels at the site for a period of eight days, using electronic water level recording instruments, allowed evaluation of the fluctuations and determination of an acceptable method of collecting site water levels. To evaluate ground water levels properly, multiple rounds of water levels had to be collected and averaged to filter the noise, or short-term fluctuations, from the water level data. Monitoring for these short-term fluctuations in ground water levels should be considered good engineering practice in any ground water investigation.