Example aspects of a nozzle cap adapter, a nozzle cap assembly, and a method for method for mounting a nozzle cap to a fire hydrant nozzle are disclosed. The nozzle cap adapter can comprise an adapter ring defining a first adapter ring end, a second adapter ring end opposite the first adapter ring end, and an interior void extending from the first adapter ring end to the second adapter ring end; a nozzle connector extending from the second end of the adapter ring, the nozzle connector configured to rotatably engage a fire hydrant nozzle; and a latch coupled to the adapter ring and configured to removably lock the nozzle cap adapter onto the fire hydrant nozzle.