Most dermatologists recommend mainly washing your face with cool or lukewarm water because the soap can strip essential oils from your faces skin.
However you still really should use soap to wash your face or some facial cleanser at least every few days to keep your skin on your face clean.
That is especially true when you're sweating more during the day or if you work someplace that gets your face dirty even without you realizing it.
What I do myself is to wash my face with soap or facial cleanser once every few days and then on the other days I use mainly water.
That is unless I have dirt on my face or am feeling sweaty then I use facial cleanser or just some soap.