The answer to 'why is my shut-off valve rusty water' is that a rusty shut-off valve is often caused by mineral buildup or corrosion in the valve over time. This can lead to discolored, rusty water coming from the valve when it's turned on. The rust may also indicate the valve is nearing the end of its lifespan and could fail soon.
Some common causes of a rusty shut-off valve include old age, hard water with high mineral content, and improper installation or maintenance. Symptoms may include difficulty turning the valve, leaks, and discolored water. In most cases, the solution is to replace the shut-off valve entirely to restore proper water flow and prevent further issues.