The answer to 'why is my water line slow draining' is that there is likely a blockage or obstruction in the plumbing system. Common causes include buildup of debris, hair, or grease in the pipes, a broken or damaged pipe, or a problem with the main sewer line.
Symptoms of a slow-draining water line include water taking longer to empty from sinks, tubs, or showers, gurgling sounds, or water backing up into other fixtures. To fix the issue, you may need to use a plunger, snake, or other tool to clear the blockage. If the problem persists, it's best to call a professional plumber to inspect the system and provide a more permanent solution.