|In many countries the water is recycled due to environmental law.
If you live in a place where salt is used to remove ice from the roads you probably want to remove the salt from your car.
Unfortunately the salt stays in the water. The more cars washed, the higher the concentration of salt will be in the water used to wash your car.
A typical sign on this problem is rust in places where you normally don't find it. That is on the top lists of the doors, roof etc.
Solution: wash your car by hand. Use environmently healthy products as far as possible.
If you have a good solution to this problem you can probably earn some money.