The answer to 'why is my shut-off valve leaking water' is that the shut-off valve is likely worn out or damaged, causing it to leak. Shut-off valves are used to control the water supply to a specific fixture or appliance, and over time, the internal components can deteriorate, leading to leaks.
Common causes of a leaking shut-off valve include mineral buildup, worn washers or O-rings, and corrosion. Symptoms of a leaking shut-off valve include dripping water, moisture around the valve, or even a steady stream of water. If the leak is severe, it can lead to water damage and higher utility bills.