Hard Water spots are very damaging to your cars paint, when left to dry. When Hard Water hits the paint surface of your car, that water bead is then hit by the sun which acts as a mini magnifying glass, and as that water bead drys the calcium, alkali, and minerals in that water bead ETCHES into your cars paint system. If you have paint protection such as a sealant, wax, or polish this will help to minimize damage, but its best to dry the hard water as quickly as possible. Always keep your vehicle polished for maximum protection from water, bugs, bird droppings, and pollution in the air that settles on your car. See more Detailing Tips on my Blog  @  Nu-Sheen Blog.com   and....KEEP EM CLEAN!
This is a picture of  the  STI Subaru after I completed the Detail. 16 man hrs to remove Hard Water spots. See above Video.

From what I have researched , both dish soaps and car wash products use the same surfactant(cleaning agent) . SLES (Sodium Lauryl Ether Sulphate), Dodecylbenzene sulphonic acid (neutralised with Sodium Hydroxide, Triethanolamine or Isopropanolamine). Concentrations will very. Dish soaps and car wash products will use different dyes and fragrances, some silicone emulsions or waxes for increased shine, mabye optical brighteners.The actual surfactants that do the cleaning will be the same,and they all use SALT TO BUMP UP THE VISCOSITY (thicken the product). Theres no such thing as a 'harsh' surfactant or a 'soft' one. " Harsh detergent" is marketing BS. No detergent is going to dissolve your acrylic clear coat. What causes more damage than anything is UV Degradation. Best advice I can give you is to use a product formulated for the specific task.
Hi I'm Chandler Professional Auto Detailer , providing Detailing tips for car owners who wish to wash,clean, and maintain the appearance of their car. After washing and drying your vehicle open one door at a time ,and fully wipe the door jamb area. This would include all around the inside of door and door hinge areas. Maby two to three times a year, spray cleaner in door hinge areas and scrub with a long brissel brush, then rinse with water using a hose or pressure washer,then dry. In my Detail Business I always wipe down the door and trunk jambs, weather its a wash or full Detail. Take notice next time you open your car door or a friends car door, look at the door jamb areas and you will see most of the time,people over look this area when cleaning their cars. For more Detailing Tips go to my Blog @ Nu-Sheen- Blog.com