There's a couple of issues here. The federal minimum wage for tipped workers is $2.13/hour from the employer, with the employer required to guarantee that they make the full minimum wage after tips are added. Some states add additional requirements, such as making the minimum wage paid by the employer for tipped employees the same as for non-tipped employees. So if you're in one of those states, you can be assured that the bartender is getting minimum wage even if nobody tips. Separate from all of that is the matter of whether minimum wage is a living wage.