A leak at the base of a sink faucet can be the result of a problem in the O ring, a worn out washer, a corroded valve seat or a worn out seal. Loose parts and broken plumbing can also cause the sink faucet to leak at the joint.
Dried-up O rings, a small disc attached to the stem screw on the faucet that holds the handle in place, cause most faucet leaks. The O ring, or the stem or cartridge, can become loose or worn out with use. Removing the worn out part and replacing it with a new one repairs the leak.
Some faucet leaks occur when the joint between the fresh water pipe and the base of the faucet becomes corroded. The accumulation of water sediments can cause a valve seat to corrode over a period of time, leading to a leaky faucet. Cleaning the valve seat regularly to prevent corrosion and replacing it when worn out can help to keep this type of leak from occurring.
The improper installation of washers and the wearing out of seals because of friction can also progressively cause the base of a faucet to leak. Other common causes include broken or cracked pipes and fittings.