The answer to 'water line constantly running' is that a continuously running water line is usually caused by a problem with the toilet or a leaky faucet. The most common issues are a stuck or malfunctioning toilet flapper, a leaky faucet washer, or a problem with the toilet fill valve. This can result in water constantly running and higher water bills.
To troubleshoot, first check the toilet by flushing and listening for the water to continue running after the tank has filled. You can also put a few drops of food coloring in the tank and see if the colored water appears in the bowl without flushing. If the toilet is the issue, you may need to replace the flapper or fill valve. For a leaky faucet, you'll likely need to replace the washers or seals. While some of these fixes can be done DIY, it's best to call a professional plumber if you're not comfortable working on plumbing fixtures to ensure the problem is properly resolved.