Check your manual first, but generally, no. Most steam mop manufacturers (like Shark or Bissell) explicitly warn against adding vinegar to the water tank. The acid can corrode the internal heating element and degrade the rubber seals, eventually causing the mop to leak or stop steaming entirely. A safer practice for reaping the benefits of both vinegar and your steam mop is to spray a diluted vinegar solution (perhaps enhanced with citrus for a fresh smell) onto the mop pad or onto the floor, and then use your steam mop as directed. This gives you the cleaning power of vinegar without risking the life of your appliance.