Observation of the long term stability of water stations in the Pierre Auger surface detector

The results of a study examining the long-term behavior of Pierre Auger surface detectors is presented. The station properties, such as water quality, liner reflectivity and the water level must be continuously monitored. Such monitoring provides information on the long-term stability of the detectors, which have been designed to operate for twenty years. Using pulse height and shapes of cosmic ray muons, water quality changes are monitored and a technique developed to identify and monitor long-term trends in the array.