An oil-water separator for separating mixed density fluids, such as oil and water, oily sediment laden water and the like, as well as portable, in-tank and towable and anchorable boom containment systems. The oil-water separator employs at least two oil-separation chambers operating in opposing but synergistic separation modes in parallel. The oil-separation chambers alternate distribution of a single mixed fluid density stream between the chambers using a partial vacuum source to draw the stream into one chamber, while concurrently stopping inflow of the stream into another chamber by removing the vacuum source. The apparatus allows each chamber to switch back and forth between (a) actively separating and removing oil when the partial vacuum is applied, and (b) passively separating oil and removing water when the partial vacuum source is removed. The oil-water separator uses include rapid deployment cleanup kits being lightweight and compact for easy transport, access and application.