An ultra-high-pressure rotary water-jet gun capable of removing rust, scale, burrs, paint film and other unwanted deposits from the surface of metal, concrete and other materials. An air turbine serves to rotate an eccentric rotor within the gun housing. A high pressure water line passing through the rotor is connected to a nozzle head on which are mounted several nozzle tips. The nozzle head is rotated in a circular path by the eccentric rotor while directing the high pressure water jets against the work piece. A pneumatic circuit and a hydraulic circuit with certain controls are provided.