Process for recirculating and purifying waste water from a vehicle washing installation

A process for purifying waste water from a vehicle washing installation comprising collecting said waste water, the water containing oil, in the first container, passing the collected waste water from the first container to a third container by negative pressure generated by a water jet pump having a water seal of purified waste water, automatically emptying water from the third container into a second container, directly or indirectly, when a predetermined amount of waste water is reached in the third container, said waste water being passed through a separator for purification, a portion of the water purified in said separator being provided for said water seal either before it enters the third container or between the third and second container,and returning the waste water from the second container to the vehicle washing installation for reuse.