Abstract: A fuel purifier for separating and removing polluting water from hydrocarbon fuels, comprising a decantation vessel having at its upper end a normally open inlet and an outlet opening and at its bottom end a second normally closed outlet opening, a source of light and a photocell arranged in opposite positions in a tubular central wall portion of the decantation vessel, and a float vertically movably mounted within the decantation vessel to normally close the path of light from the source of light to the photocell, but adapted to move under the action of the water accumulating at the bottom of the decantation vessel to an upper position in which the photocell receives light from the source of light to open the second outlet opening to drain the water.