Causes: Worn out valves, seats and gaskets are common culprits. "Turning faucets on and off over the years wears these parts out," Hogan says. A faucet valve cartridge can also be to blame.

Start your search inside. Many shut-off valves are located in easy-to-access areas indoors. If yours is, it should only take a couple of minutes to find it. The main water shut-off valves are ...