Wash your hands for 20 seconds, as long as it takes to sing "Happy Birthday" twice - Mayo Clinic video

From Mayo Clinic: Running your hands under the faucet with some soap for a few seconds isn't enough to kill germs.

To help avoid catching the flu and other illnesses, wash your hands thoroughly and frequently with soap and warm water or alcohol-based hand sanitizer, particularly before leaving a restroom, eating or touching your face.

Wash your hands for about 20 seconds, about as long as it takes to sing "Happy Birthday" twice. When visiting a public restroom, use a paper towel to turn off the faucet and open the door when leaving.