How can I fix a leaky bathroom faucet with a single handle?

To fix a leaky bathroom faucet with a single handle, you can start by turning off the water supply to the faucet. Then, remove the handle and the cartridge inside the faucet. Check for any worn out or damaged parts, such as the O-rings or seals, and replace them if necessary. Reassemble the faucet and turn the water supply back on to test for leaks.