Abstract: The present invention is directed toward an anti-tamper system for fire hydrants that prevents intentional introduction of contaminates into the water system as well as prevents unauthorized removal of water from the water system while still providing easy access to pressurized water by authorized personnel. The system is constructed and arranged to prevent the rotation of the valve stem and/or the nozzle cap(s) by unauthorized users. The system replaces or modifies the valve stem to include at least one aperture therethrough. A replacement nozzle cap is also provided. The nozzle cap includes a centrally located locking bar that cooperates with both the valve stem and the nozzle cap to prevent rotation thereof by unauthorized persons. A release tool is provided to remove or retract the locking bar from the valve stem, to allow valve operation, while simultaneously allowing rotation of the nozzle cap to allow removal thereof from the outlet port.