An interesting thing here is that in some places, "Power washers" can still be legal even when hosing bans are in place.
You suds up the car with a sponge and just blow it off with a Karcher or Gerni or similar.
Reason being that they only use a fraction of the water of a standard hose and it all happens so quickly.
As an example, where I live there's no reticulated water supply so we have to collect and store our own water (currently around 11,000 gallons storage but used to be only 5,000 for a family of 5 prior to installing second tank) so it goes without saying we soon became expert at conserving water. The Karcher is always used for any volume washing, such as cars, boats and walls and windows in the house. In your cases, it should be a good way of washing the salt off the undersides too.
This is worth a read:
http://www.karcher.com.au/aus/Watersaving.htm
Alan S
By the time you're old enough to know it all, you can't remember why you were learning.