This article describes a deaerator, developed in California, to furnish oxygen‐free water to low‐pressure boilers and hot‐water systems where other types are impracticable. Oxygen removal is accomplished by passing the water through a tank upon the surface of which hydrogen is deposited by electrolysis. Dissolved oxygen acts as a depolariser and is reduced first to hydrogen peroxide and then to water. The anode and cathode are made of aluminium alloy.