so after reading this thread , I decided to experiment , and no better time than during this hot weather.
I am DI only as my tap TDS is hovering around 50 and this is the caser for the area my customers are based .
so I have been cleaning windows with a tds of 25 to 30 for about two weeks .
I have done this by filling a part of my tank with tap water, and then filling the rest with pure 00 TDS
As the windows have been drying extremely quickly , on most houses I have been able to guage the results .
as of yet I have had no issues apart from a first clean . ( I carry a few barrels off 000 TDS just incase.
One thing I will add is that I have a good flow rate to be confident in the rinsing.
This has been just experimenting, I wont be continuing like this . but it has given me confidence that 30 TDS is workable