You won't get much volume.
Air expands, so there seems to be a lot more of it. Water doesn't.

Air would increase the pressure in short bursts. just like using a water hose with air trapped in the hose. As bill says when the air comes out if will over take the water. but, what water comes out is at a higher force. IMO using short bursts would create higher pressure, but why not just use a pressure washer, entry level models are reasonable cheap and used ones or ebay ones are alot cheaper IMO..