The answer to 'shut-off valve leaking water' is that a leaking shut-off valve is a common plumbing issue that can have several potential causes, including worn washers, corrosion, or a faulty valve mechanism. Symptoms may include water dripping from the valve or pooling around the base. In many cases, this can be a DIY fix, but there are also times when calling a professional plumber is the best course of action.
If the leak is minor and the valve is relatively accessible, you may be able to tighten the packing nut or replace the washers yourself. However, if the valve is stuck, the leak is significant, or you're not comfortable working on plumbing, it's best to call in a licensed plumber. They can properly diagnose the issue and make the necessary repairs or replacement to stop the leak.