I have seen an entire building of glass covered by silica spots from a WFP. The TDS on the meter had showed 0 or maybe 1. TDS meters cannot show silica in the water. So how do we detect it and how do we keep it from spotting? Further did you know that even pure water can have an unbalanced pH without any minerals present at all. Exactly how does pH affect the reaction between water and a glass surface? The relative humidity is already 100%. Over 90%. So it would seam the glass surface is already compromised. Especially if the glass is very hot. Remember those papers that Penn Tech produced for the Glass Committee of the IWCA?
Once all your minerals, “and silica” have been removed simply work on cool glass out of the sun on an overcast day. You will know how “raw” the surface is by how your water moves over the surface. Here is one for you PA. It is all about flow.
As for the white papers as Paul West calls them just go to the IWCA Glass Committee and ask them. There was some fantastic science performed at that time!