We describe the use of a water Cherenkov detector to study the distributions of charge, amplitude and rise time of the signals associated to isolated electromagnetic particles, isolated muons and extended air showers in the secondary cosmic‐ray radiation. The detector consists of a polyethylene tank of 1.54 m of diameter filled with water up to a height of 1.2 with one 8″ phototube looking downwards in the center of the tank at the level of the water. The data acquisition system consists of NIM modules, one digital oscilloscope and one PC running LabView. We performed precise measurements of voltage amplitude, charge deposition, 10&percent;–90&percent; and 10&percent;–50&percent; rise times to each of the WCD signals for three different types of triggers:vertical non‐central muon, vertical central muonsandarbitrary muons. We show the existence of very strong correlations among these parameters in the signals corresponding to isolated electrons, isolated muons, muon interactions with the PMT glass envelope and extensive air showers. These correlations allow a clear separation of these components when one uses bi‐dimensional plots such as charge vs amplitude, charge vs rise time and charge vs charge/amplitude. We use our results to suggest a way in which one can measure &mgr;/EM in large ground arrays of water Cherenkov detectors such as in the case of the Pierre Auger Observatory. © 2003 American Institute of Physics