Using a good quality car wax is the first thing you need to do. Car wax forms a protective layer around the cars body thus effectively preventing hard water spots. Car wax also helps keep moisture off the car so any impurities in the air will not be able to aid in the formation of hard water spots.
After you are done washing your car, the best idea is to let dry in shade and do not leave it in the sun. But if you have no choice and must leave the car under the sun, the best shot you have at preventing hard water spots is to completely dry the car using a piece of cloth and not to leave any water on the cars body.
Waterless car wash is an extremely efficient way to avoid water spots. In a waterless car wash, chemicals are used to clean the car’s body instead of hard water. When there is no water being used, there will be no chances of water spots.
Sealants can be an effective means of preventing hard water spots. Sealants form a protective layer around the car’s body. Apart from preventing damage to the car’s paint, sealants do not let water droplets stay on the car’s body, thus preventing hard water spots effectively.
You can use car polish or a mild polishing compound to avoid formation of water spots.