The answer to 'why is my bathtub constantly running' is that there is likely an issue with the bathtub's drain mechanism or plumbing. The most common causes are a worn-out flapper valve, a stuck stopper, or a problem with the drain pipe or trap.
A constantly running bathtub can waste a significant amount of water and lead to higher utility bills. It's important to address the issue promptly to prevent water damage and potential mold growth. While some basic troubleshooting and minor repairs can be done DIY, it's generally best to call a professional plumber if the issue persists or you're not comfortable working on the plumbing.