Water spots are generally the result of ground water that has dried on a vehicles finish. Ground water has minerals and other things such as iron oxide (rust) so when the water evaporates on the body...
Depending on the type of water, this can be a tough job. Some of the products other people have found valuable are Rain-X (to protect before the spots happen), Spot-X, C-30 Water Spot remover, Zaino...
removing water spots on paint finish.
You might try disolving 3 tablespoons of baking soda in a bucket of warm water; lightly sponge on vehicle , rinse then wash. be sure to towel dry to avoid new...