This is a picture of a building we clean the windows and metal facade with DI clean water. We dont need much pressure so I use a little 12hp at 3000psi cold water machine. Run the hose from the spicket through the DI bottle which then feeds to the pressure washer, which then sprays purified water onto the windows and building. We usually go through 3-4 DI tanks and it takes 8hrs to wash the entire building. THe 3-4 tanks ensures the water stays as close to clean as it can be. The water dries clean on the building and windows as long as the first rinse removes most of the dirt. THe second rinse removes the last bit of dirt/residue and all is good.
Another couple buildings DI water and pressure wash. Wash windows and building facade, use DI water so everything dries nice and clean. Spend maybe 3-4 hours at end of project going over a few spots that water drips from window trim and leaves spotting. All these buildings pictured are 3-5 stories so they don't have davits on the roof for scaffold. The only way, I have figured to clean windows is from a lift and using the DI water. This work is good money and quick once the crew and operators get a few under their belts.
