Zinc oxide is a substance used to galvanize metal surfaces. It is highly resistant to corrosion and stays on the metal for long periods of time without the need for reapplication. However, standing water on the zinc oxide can cause it to corrode, leaving a film of white powder. This corrosion stain is known as wet storage stain. Like all corrosion, it should be removed immediately. Things You'll NeedNylon scrub brushRust-dissolving cleaning product, lime juice or white vinegarRemove any items sitting on top of the galvanized metal surface. Wait for the wet stain to dry so that the corrosion stain can harden. Scour the stain away with a nylon scrub brush. Pour a cleaning product directly onto the stain if it does not disappear after using the nylon brush. Use a rust-dissolving cleaning product, lime juice or white vinegar. Scrub the cleaning product into the stained area with the nylon brush. Rinse the metal surface thoroughly with water. Allow the area to air-dry completely before placing objects back onto the metal surface. If you missed a spot, the corrosion stain will harden again. If necessary, perform Steps 2 through 5 again. The best way to protect the zinc oxide coating is by preventing the wet storage stains from appearing. Clean the metal surface frequently and keep it dry. Also provide adequate air flow to the surface. If the wet storage stain is very large or cannot come off in one cleaning, contact a professional. Only use commercial, rust-dissolving cleaning products outdoors. Using these products may require the use of protective gear, such as work gloves and safety goggles. Keep commercial cleaning products out of the reach of children.