Lately, due to the wet weather, many car owners have mentioned about problems caused by stubborn watermarks.
This problem plagues many car owners, but does not seem to happen to others. It mainly depends on the environmental pollutants where you park your car daily.
Traditionally, when you have w.mark problems, the solution was to use abrasive compounds, polishes etc etc to abrade it off.
Done properly, its ok..but time-consuming.
Done improperly, it's also ok....but with lots of swirls and other problems.
Now, there are local companies promoting DIY chemicals that are sprayed onto the paint surface, where the liquid will turn into purple, and you just hose it off. Presto! no more water marks!!
But hold on...there's no such thing as a free lunch.
These chemicals are nothing new,and was used mainly in many rim cleaners. It's based on ammonium thioglycolate and upon contact with specific contaminants, it turns purple, and must be flushed away properly. Ammonium thioglycolate is used in hairsalon products (especially perming solutions) and that explains the pungent ammonia smell.
These strong chemicals cannot touch any glass or uncoated aluminium surface, and even worse, if these surfaces already have pits, chips or microscopic scratches/cracks. The chemical could permanently damage these surfaces. In the US, these products are packaged as "waterstain removers for household use eg shower screens etc etc)" and carries elaborate warnings about potential damage to certain surfaces/materials.
Now, many of these products hv been re-packaged and re-positioned as being suitable for car paints. So, if you come across these seemingly amazing wonder-products, pls be careful. If you really wanna use it, always make sure there's running water next to you, and keep on flushing with water as you apply the product to minimise contact time with the paint and surrounding surfaces.
.Are we suppost to wipe the waterspot each time after rain?sound like impossible 
,that mean must wash more fequantly to prevent it la..