The Pierre Auger Observatory is a hybrid cosmic ray detector consisting of 24 fluorescence telescopes to measure the fluorescence light of extensive air showers complemented by 1600 water Cherenkov detectors to determine the particle densities at ground. A SD stations consist of a 3.6 m diameter tank containing a sealed liner with a reflective inner surface. This one is filled with 12000 liters of pure water. Shower particles pass through the water and produce Cherenkov light, that is collected by three nine-inch-diameter photomultiplier tubes that are symmetrically distributed at a distance of 1.20 m from the center of the tank and look downwards through windows of clear polyethylene into the water. The station has also a solar power system, which provides an average of 10 Watts for the PMTs, and electronics package consisting of a processor, GPS receiver, radio transceiver and power controller.