Http://kafila.org/what-are-the-causes-of-leaky-faucets/

Leaky faucets can be frustrating and wasteful. But what causes them to leak in the first place?

Causes of Leaking Faucets:

Clogged Aerators: A clogged aerator can reduce water flow and cause leaks. To fix, clean or replace the aerator according to the manufacturer's instructions.
Loose Fittings: Loose connections between pipes, valves, and faucets can allow water to escape. Tighten any loose fittings to ensure a secure connection.
Worn-Out O-Rings or Gaskets: Over time, O-rings and gaskets can wear out, causing leaks. Inspect your faucet's parts for signs of wear and replace as needed.
Cracked or Damaged Faucet Parts: Cracks in the faucet's body or parts like handles or stems can allow water to leak. If you suspect damage, consult a professional plumber for assistance.