The answer to 'water line constantly running' is that there are several common causes, including a leaky faucet, a problem with the toilet, or an issue with the water heater. The most common symptom is the sound of running water or a higher-than-normal water bill. Solutions can range from simple DIY fixes to more complex professional repairs, depending on the underlying cause.
If the leak is coming from a faucet or toilet, you may be able to fix it yourself by replacing washers or other small parts. However, if the leak is in the main water line or there's a problem with the water heater, it's best to call a professional plumber to diagnose and repair the issue.