The answer to 'why is my faucet leaking water' is that a leaky faucet is usually caused by worn washers, worn seals, or a damaged faucet cartridge. Over time, the rubber or plastic components inside the faucet can become brittle and cracked, allowing water to slowly drip out. This is a very common plumbing issue that most homeowners can fix themselves with a basic faucet repair kit.
If the leak is coming from around the base of the faucet, it may indicate a problem with the faucet stem or the faucet seat and spring. These internal components can also wear out over time, causing a leak. Replacing the faucet stem or cartridge is usually a straightforward DIY repair, but if you're not comfortable doing it yourself, it's best to call a professional plumber.