When water dries in your home on your shower screen or kitchen and bathroom surfaces you will typically find water spots left behind. These left untreated overtime can create a build-up of limescale and eventually damage the surface. This is a problem we are all too aware of within the home, but we don't recognise as much on our cars. Water spot marks on a car happen because of impurities in rain and hose water. If left untreated, just like in your home, the chemicals can etch into the car's paintwork, leaving marks that no car shampoo will remove.
The fantastic news for those that can keep on top of it, you don't need a machine polisher or spend hours trying to remove them. A water spot remover for cars is specifically designed to safely remove water spots. They achieve this with a mild chemical reaction to break down the limescale. If the waterspot has been left on too long it can cause etching, the slight acidity of rain water along with the heat from the sun as a catalyst creates ring marks within the car's lacquer. This will need polishing out to be removed, so it is best to avoid this step with just a quick waterspot remover after every few washes.
Another great advantage of water spot removers is to restore ceramic coatings and reinvigorate any self-cleaning hydrophobic function. It is to be noted to check the brand of coating before proceeding but many times when a ceramic coating stops beading as it did on the first day it is most likely "clogged" with water spots; sometimes not visible but certainly enough to increase water tension on the surface. A light wipe over with a mild waterspot remover and bingo the ceramic can be as good as new.
A normal house-hold limescale remover would be far to aggress for your car's paintwork and especially any plastic and rubber seals. Within one wash you could permanently damage these surface with no fix apart from a full repair. You can use a dedicated car waterspot remover, which will have a milder chemical to achieve the same result and be safe on your car's paintwork.