The answer to 'how to maintain supply lines' is to regularly inspect and clean your plumbing supply lines to ensure they are functioning properly and prevent leaks or other issues. This includes checking the lines for any cracks, holes, or wear and tear, and cleaning out any buildup or debris that may have accumulated.
It's recommended to inspect your supply lines at least once a year, or more frequently if you notice any issues. You can do this yourself by visually inspecting the lines and using a flashlight to check for any problems. If you do find any issues, it's best to call a professional plumber to make the necessary repairs.