Abstract: A tamper proof water-tight well cap has been developed to seal the outflow pipe of wells or tanks. The well cap includes a first member coaxially fitting over the outflow pipe having a plurality of peripherally arranged threaded bolt collars to receive and hold bolts. An annular collar member having a plurality of hollow bosses to accommodate bolts is arrayed on the outside circumferential surface of the annular collar member and the collar member has a plurality of radially inwardly extending tabs arranged about its inner circumferential surface. An annular compressible sealing member connects the first base member and the annular collar member to prevent any leakage of liquids into the well or tank. A plurality of bolts fitting through the openings in the bosses on the collar member are threaded into the bolt collars on the base member to hold both parts together.