The answer to 'why is my pressure regulator rusty water' is that a rusty pressure regulator is often caused by mineral buildup or corrosion within the regulator. This can lead to discolored, rust-colored water coming from your faucets and appliances. Symptoms include low water pressure, leaks, and a malfunctioning regulator.
To fix this, you may need to replace the pressure regulator, which is a relatively simple DIY repair if you have basic plumbing skills. However, if you're not comfortable working on plumbing components, it's best to call in a professional plumber to diagnose and replace the regulator.