Abstract: Apparatus for purification of oil contaminated water, particularly of reservoir water from oil production, comprising a depression for receiving the contaminated water, wherein a first partial separation of oil particles and water is carried out within the depression, so that, on the one hand, the oil and, on the other hand, the water reduced in oil content are drained off from the depression, wherein the oil content-reduced water is guided from the depression to an ultrafiltration device, wherein a precipitant is added to the oil content-reduced water before introducing the oil content-reduced water into the ultrafiltration device, and wherein the oil content-reduced water in the ultrafiltration device is separated into a clearwater phase and an oil-enriched phase using a membrane made of polymers, and wherein the oil-enriched phase is guided back to the depression, and the clarification water phase is drained off.