Why do water spots come back after I remove them?

They may reappear because the underlying etching was never removed, because the vehicle is repeatedly exposed to hard water and allowed to air-dry, or because a glaze, wax or detail spray was temporarily hiding the marks until it washed away. Identify the source of the water, such as sprinklers, a hard-water hose or a dripping tree, and dry the car promptly after washing or rain.