You know, technically speaking, if you are on a domestic well you are not allowed to wash your car. (Unless, I suppose, you can get it into your house.) Denver Water owns all the water up here and they could cut off your well. That being said, I do it ocasionally myself and Denver Water has never shown up.
Yeah, I was confused for a long time - to me domestic and household should be the same, but my well permit tells me different. Besides when I wash my car, it just runs right back down to the well.