The answer to 'why is my faucet constantly running' is that there is likely an issue with the faucet's internal components, such as a worn-out washer or a faulty valve. A constantly running faucet can waste a significant amount of water and increase your utility bills.
Some common causes of a constantly running faucet include a worn-out rubber washer, a problem with the faucet's cartridge or valve mechanism, or a buildup of mineral deposits. In many cases, the solution is a simple faucet repair that can be done by a homeowner, but in some cases, it may require the expertise of a professional plumber.