I think the water pump is included with your super charger belt. I know that newer Bonnies have the water pump attached to the other belt and you could run without it for a little while but with real bad gas mileage.
I am not sure if you could just get a smaller belt and run your water pump though maybe possible. I know that you could ask BillBoost or Danthurs and they would be able to tell you for sure. Good luck and sorry I wasn't able to give you 100% here but I think you'll find the answer you are looking for.
1994 SSEi Fire Red New License plates soon BURNT 94