Abstract: A ship typically is constructed with an outer hull, and an inner hull which defines the usable space of the ship. Between the outer hull, and the inner hull, the ship will generally have a low point, or bilge, for collection of any water which gets onto the ship. Therefore, one of the chambers of the ship can preferably be outfitted with processing equipment for cleaning the bilge water. The apparatus and associated method for cleaning the bilge water generally involves at least a gravity separation in a gravity separation chamber to separate at least some oil from the bilge water. Since a gravity separation is generally not sufficient to produce environmentally safe water, the ship can also be equipped with a further filtering arrangement for further processing of the bilge water.