Depending on how cold your winters get and how far you have to pipe the water, you may suffer a huge loss of hot water. You might want to consider a small water heater for the garage. In either case, you will have to keep some heat in the garage during the winter. I have a similar situation, and I keep my shop furnace at 55 which is the lowest it will go, during the winter. It's easy to bring it up to comfortable temperature when I want to work out there, and it sure is nice to have a reasonably warm car on icy mornings. Garage is well insulated, but there is obviously some expense involved. I have a NG overhead furnace.