Some extension cords are manufactured for water resistance. They are waterproof, immersible or safe to use in standing or flowing water. Any mention of water resistance merely indicates the vinyl or rubber that serves as the exterior covering of the cord will not allow water to soak through to the wires. Any cracks or breakage allows water to penetrate. The Occupational Safety and Health Administration (OSHA) warns that extension cords and the cords of portable electric equipment be frequently checked for signs of damage. Water resistant cords are heavy-duty industrial cords. Standard household extension cords white, green or brown in color are not water resistant.
Never plug any extension cord into an electric source when either one of the plug ends are wet. Never plug into an electric source with wet hands or come in contact with, or use, any electrical items while standing in water. Other liquids are just as conductive as water posing the same electrical shock hazards.
Exposing extension cords to moisture shortens the usable life of the cord. Once moisture, including humidity, comes in contact with copper wiring, corrosive build-up forms and travels along the cord. Corrosion damages the wires, rendering the cord useless.