Hard water stains develop on your vehicle when your car is exposed to a rainy day or a dirty car wash. The mineral deposits that make contact with your car's paint leave behind unattractive, cloudy water marks that are not always easy to remove. The key is to use a cleaning solution that will remove the hard water stains without harming the auto paint and without leaving cleaning solution film behind.
Fill a spray bottle with equal parts warm water and white vinegar.
Fill a cleaning bucket with 1 gallon warm water and 2 tbsp car wash soap.
Spray the water-and-vinegar solution onto a 2-foot square section of your auto paint.
Wipe the area immediately after spraying with a cleaning rag soaked in the car wash soap.
Repeat until you have worked your way over the entire car, and also clean the remaining parts of your vehicle with the car wash soap routine as well to give an even cleaning to the entire car.
Rinse the car with your garden hose, and hand-dry with clean rags to prevent new hard water stains from forming.
Apply a fresh coat of car wax to restore shine to the auto paint, following the application instructions on the car wax container.