Do you know the differences between water repellence, hydrophobic effect and hydrophilic effect? These are words to describe the level that wax and coating agent repel water. Chose your favorite type.
Water drops bounce right off the body.
Water glides off and drains smoothly.
Water remains on the surface like a film.
Rain deposits and chlorkalk contained in tap water adhere to the car body, as water drops evaporate on the surface. That's the ion deposit. On the other hand, water spot is a tiny dent caused by water drops that concentrate sunlight like a magnifying glass. Some are caused by acid rain. In the worst scenario, it may be fixed only by repainting. Today's paint surfaces are very advanced, but it's better to dry the car thoroughly every time after raining or washing the car.