The thing is that Gary999's water may be fine at 30 ppm because his water contains only a certain type of mineral and not say lime.
People don't seem to realise that someone's water that reads 010 in wales won't be the see to someone's 010 water that lives in Birmingham.
I guarantee that someone's water in Birmingham at 030 would leave spots because of the limescale in the water.
That's probably why Gary gets away with 100ppm because his water is of a very good quality.
The water from here is of good quality it comes from wales
I would have no problems using water at 100ppm deliberately but
would dry every pane before the water evaporated and any sediments
are left behind.
normally i try to use rainwater at around 14ppm and dont have any
problems apart from the odd occasional window which i dry,most of
the year my tap water is around 30ish and have very few problems
but i know my round.
On new work i tend to dry every pane of glass afterwards anyway
like to be 100% sure of results i have become very proficient at drying
glass up to third floor..after a couple of cleans i normally revert to
my normal routine