your water is slightly acidic and/or has mineral buildup. simple fix if it is minerals clean grout with a solution 50% up to 100%vinegar ,flush with water .if clean,seal grout,if not,repair grout ,seal thoroughly. JMHO marvin
The last of the big spenders,world traveler,international jetsetter,Oil wells drilled,wars started,Virgins converted,Governments overthrown,Revolutions started,governments run,EX_WIVES HOUSEBROKEN,(NO warranty on this last service due to low success rate)PS.That Petrol in your car probably came from a hole in the ground I drilled!! MARVIN DIY'selfer Extroidanare!!!