[Gregorio]

Steel wool and abrasives are not the answer. Aside from adding miniscule scratches, they wear down the surrounding substrate as you grind away at the offending buildup. You are left with tiny "islands" in the surface. Clay bar and lube is a much safer alternative. If you want something in a bottle, Lime Away bathroom cleaner works very well on water spots. Acidic like vinegar but much stronger. I have been using it on all my cars and boats for years.

 

[Gregorio]

Looks like expensive gravel with vinegar, lime away and lemon juice.