Water Cherenkov Detectors (WCDs) play an essential role in space weather and cosmic rays studies around the world. In this article, we present a general methodology to calibrate a WCD based finding its optimum operation point and counting the delay time of the transmission cables. The dynode charge histogram of the WCD and CORSIKA simulations validate this methodology. Finally, to illustrate the capability of WCD tomeasure fluctuations in the secondary CR flux, we studied the 07.09.2017 Forbush and compared our measurements with data obtained from the Neutron Flux Monitor at UNAM and the Kyoto Dst index service.