Are you wanting this because you don't want to dry the car? If you're drying the car off, paying anything to achieve 'pure' rinse water is a waste.
When I wash in the driveway, I remove the spray nozzle from the hose and let the water run freely over the entire car. The stream of water takes most of the standing water with it, so there's very little water left on the car itself. Cuts drying time way down.
After towel drying, I use the leaf blower to get the water out of all the seams & joints, then do a final wipedown. This prevents hard water deposits from accumulating in the hard-to-reach areas. A tip for the blower: I place a used dryer sheet over the air intake grille to prevent anything from being sucked in and blown onto the car.