I assumed that we were talking about "normal" tap water of the sort that most people in the western world are happy to drink. Not from Flint MI or holding all sorts of organic matter in suspension.



I live in an area of the UK that has hard water and it does indeed leave white spots if allowed to dry on a car. But to put it into perspective that sort of water has perhaps 500mg of dissolved minerals per litre. So by weight 0.05% minerals and the rest good old H20. Negligible, no?


But if using demineralised or distilled water floats your boat knock yourself out - it won't do any harm.