DH unit removes from oil the water content, causing malfunctions of various hydraulic machines, thereby increasing the availability factor of machines. When oil contains water, the electrostatic dust cleaner (EDC) determines it is no good, and so it stops working. Water contained in oil initiates rusting of metals by adhering itself to the metal surface. The rusts are released into oils and act as catalysts to accelerate oxidation reaction of oils, i.e., presence of water makes oxidation rate by a few tens to a few hundreds of times. To solve this problem, we developed the DH unit that separates out water content. We manufacture two types, water-absorption and water-separation type.