First introduced in 1967 by the DuPont Corporation, Corian is a synthetic acrylic material filled with aluminum trihydride. At first, it was used only in vanity tops and sheets; over the years, however, it has taken on all kinds of applications. Sinks, design elements, light fixtures and many other items around the home can all be made with Corian. Still, its primary use is as a countertop material, to replace marble or granite. One of its major benefits is the ease of cleaning stains from Corian surfaces.
Apply some dish soap to a sponge, rinse it lightly with warm water and use some elbow grease to get the stains out.
If that doesn't suffice, treat the stain with a standard ammonia-based household cleaner. Don't use window cleaner, as it may alter the surface of your Corian counter.
Dry thoroughly with paper towel when you're finished. If standing water dries on Corian, it can leave behind a blotchy residue mark.
Remove water stains on your Corian counter with any product designed for treating hard water marks.