Driver was moving his empty (Community Aid) Brine water tanker from location after rigging down job. When attempting to move the truck off location an unusual noise was heard by the driver. The driver looked back through mirror and saw the tanker moving left when the prime mover was turning right off location. The driver Steered back to the left to get back under the tanker. In order to maintain control of the prime mover and tanker he steered and applied brake pressure as necessary bringing the vehicle to a stop. The trailer sustained small damage to the legs and cross member. The cause for the separation is due the King Pin Nuts coming off which holds the Flange like configuration on the Trailer.