Wash your car by hand without wasting water it is possible, not very difficult and also very economic in water.
At home, with only 4 cans of 5 liters of preferably non-potable water, a sponge and a biodegradable detergent, I can easily wash my self effectively while avoiding wasting a lot of water!
Also consider waterless car washing at a specialist.
You should know that by washing your car at home without paying attention, I can consume up to 500 liters of water. Not very economical as a car wash.
A zero-waste car wash uses only 20 liters of water, compared to 300 liters for a roller wash, or 60 liters of water for a high-pressure wash.
Washing your car yourself without wasting water is a good clever trick to use less water at home and save a car wash at a specialist.