Water spotting is caused my minerals such as calcium, lime, and iron in the water supply fusing to the microscopic pores of the glass. This happens when the water droplets are left on the glass after showering – the water evaporates leaving the minerals. Over time these minerals block the clarity of the glass. Specialist abrasive products (and a lot of elbow grease) are required to remove these minerals without damaging the glass. In most cases we can restore 80%-90% of the clarity, but occasionally the glass is unable to be restored.
The best way to minimise water marks is to dry the glass after each use.