The answer to 'why is my faucet leaking water' is that a leaking faucet is typically caused by worn or damaged internal components, such as washers, O-rings, or seals. Over time, these parts can become worn down, allowing water to escape through the faucet. Symptoms of a leaking faucet include dripping or constant water flow, even when the faucet is turned off.
In many cases, a leaking faucet can be fixed with a simple DIY repair. This may involve replacing the washers or O-rings, or tightening the faucet stem. However, if the issue is more complex, such as a problem with the faucet cartridge or valve, it's best to call a professional plumber to diagnose and repair the issue.