We have very hard water here too. Keep the car well waxed and then do the following as a final rinse: Take the nozzle off the hose and turn the water pressure down to about the half way mark. Now hold the end of the hose close to and parallel to the various body panels for a final rinse. On a well waxed car this will sheet 80 - 90% of the water off the surface so you aren't trying to dry those billion little beads of water.

Follow that up with a waffle weave microfiber drying towel and you'll dry the car in no time.