A bottle cap assembly, comprising a main portion, and a lid. The main portion and lid are attached by a hinge. The main portion is selectively secured to the lid with a latch, the latch opposite the hinge. The main portion has a central bore, and the hinge has a plug which fits in the central bore when the cap is closed. The central bore has internal grooves, and the plug has protuberances which match the internal grooves to effect a tight seal between the central bore and plug. The main portion further has an upper groove, and the lid has a ring which fits in the upper groove. The ring is larger in diameter and concentric with the plug. At least one opening preventer attaches between the lid and main portion to prevent inadvertant opening of the bottle and for revealing tampering to the bottle, since the opening preventer can be opened once, and then cannot be restored.