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Guide · Window Cleaning
If you've watched a window cleaner scrub a third-storey pane from the ground with a long pole and no squeegee — and then just walk away leaving it soaking wet — you've seen water-fed pole (WFP) cleaning. Here's exactly how it works, and why the glass dries perfectly clear.
Traditional window cleaning uses soap and a squeegee. The soap breaks the surface tension, and the squeegee physically drags the dirty water off the glass so it can't dry and spot. It works — but it means a ladder for anything above the ground floor.
Water-fed pole cleaning flips the approach. Instead of removing every drop before it dries, it uses pure water — water with all its dissolved minerals stripped out. A soft brush on the end of a telescopic pole agitates the dirt, a flow of pure water rinses it away, and the glass is left to air-dry. Because the water is pure, there's nothing left behind to form a spot.
Tap water carries dissolved solids — calcium, magnesium, salts, and other minerals — measured in parts per million (ppm) of Total Dissolved Solids (TDS). A TDS meter is a cheap pen that reads this instantly. Ordinary tap water in our area typically runs anywhere from roughly 100 to 400+ ppm. When that water dries on glass, those solids stay behind as the white, cloudy spotting everyone recognises.
Purify the water down toward 0 ppm and there's nothing left to deposit. As a rule, professionals want water under about 10 ppm at the brush, and ideally 000 straight off the resin. That reading is the whole game — it's why we check the TDS meter before every job.
There are two ways to get there, often used together:
RO pushes tap water through a semi-permeable membrane that blocks the vast majority of dissolved minerals, sending the pure water on and the concentrated "waste" to drain. RO does the heavy lifting cheaply, dropping a 300 ppm supply down to single digits.
A DI vessel is filled with ion-exchange resin that swaps the remaining mineral ions for hydrogen and hydroxide ions — polishing the water the final step down to a true 0 ppm. Many systems run tap water through RO first, then a DI polishing tank, so the expensive resin lasts far longer.
Pure water isn't just neutral, it's actively useful. Having had its mineral content stripped out, it's chemically unstable and wants to grab onto dissolved solids again — it's sometimes called "aggressive" or "hungry" water. On the glass, that means it actively pulls dirt and mineral residue into solution so it can be rinsed away, no detergent required.
Glass is also naturally hydrophilic — water sheets across it rather than beading up. A generous final rinse of pure water sheets down the pane, carrying the loosened dirt with it, and what's left evaporates clean.
Spots are the dissolved minerals left behind when water evaporates. Pure water has those minerals removed, so there's nothing left on the glass to dry into a spot.
Aim for under about 10 ppm at the brush, and ideally 0 ppm straight off the DI resin. A TDS meter confirms it in seconds.
Yes — that's a big part of the point. The pole reaches upper glass from the ground, removing the fall risk of ladder work at height.