Water stains develop when you leave a glass of water on your aluminum surface, or if hard water dries on the surface of the aluminum. Water stains on aluminum could appear lighter or darker than the aluminum surface. Hard-water stains will also look chalky. Regardless of the appearance of the stain, it will mar your aluminum surface. You can remove it using careful cleaning techniques that will not damage the metal surface.
Wet the aluminum surface.
Apply 1 drop of liquid dish soap to the aluminum water stain.
Scrub the stains with superfine steel wool. Do not use coarse steel wool, as it will damage the aluminum surface.
Soak a clean cloth in white vinegar if the water stains are still visible.
Lay the cloth over the water stain and let it soak for 20 minutes. This acidic solution will help remove any alkaline hard-water stains.
Rinse the aluminum with clear water and dry it completely. Do not let it air-dry, as it will show streaks.