What is pure water window cleaning, and how does it actually work?
If you have watched a window cleaner in Telford working off a long pole instead of a bucket and squeegee, the reason is the water. Here is what pure water actually is, how it is made, and why it leaves glass clear when tap water would not.
What makes water "pure"
Tap water looks clear, but it is carrying dissolved minerals and salts. In and around Telford that is mostly calcium and magnesium, the same hardness that furs up your kettle, plus sodium, chlorides, sulphates and the chlorine added to keep it safe to drink. All of it is harmless to you. All of it is left behind on your glass when the water dries, which is exactly what a spot is.
Pure water has had virtually all of that stripped out. When it evaporates there is nothing left to deposit, so the glass dries clear.
How it is made: reverse osmosis, in plain English
The main stage is reverse osmosis. Picture a filter so fine that only water molecules get through it. Tap water is pushed against that membrane under pressure. The water passes; the minerals and salts do not, and are flushed away.
A second stage called deionisation polishes off whatever traces survived, using a resin that grabs the last of the dissolved solids. What comes out the other side is about as close to pure H₂O as you can practically get in a van.
Why pure water cleans better, not just differently
Pure water is often described as hungry, and that is a fair way to put it. Having had its minerals removed, it has a strong tendency to pull other substances into itself. Applied to glass with a soft brush, it actively lifts dirt, dust and pollution rather than just pushing it about.
The comparison that makes it click: a dry sponge soaks up far more than one that is already half full. Ordinary water arrives half full of minerals, so it has less room for your dirt. Pure water arrives empty.
Once the brush has lifted the grime into the water, a thorough rinse carries it off the glass. Nothing is left behind as it dries.
The part most people notice later: soapy water leaves a thin film of detergent on the glass. It looks perfect the day it is done, then that film starts collecting dust, and the first proper rain reacts with what is left and spots the window. Pure water leaves no film, so the glass stays clean for longer and rain behaves like rain.
How purity is measured: the TDS meter
Every professional using this system carries a TDS meter, a small handheld device measuring Total Dissolved Solids in parts per million.
- UK tap water: usually 100 to 400 ppm, and the harder Midlands supply sits toward the upper end of that.
- Water fit for cleaning windows: 0 ppm, or as near as makes no difference.
It is not a marketing number. If the meter creeps up, the resin needs changing, and carrying on regardless would spot every window on the round.
What it looks like at your house
- The van arrives with a tank of pure water already made.
- A carbon fibre pole with a soft brush head connects to the tank.
- Water is pumped up the pole and out through the brush.
- The brush scrubs the glass, frames, sills and trickle vents while the pure water rinses.
- Everything is done from the ground, so no ladder goes anywhere near your walls or gutters.
- The windows are left wet on purpose. As they dry, the finish appears.
That last point catches people out. Judge the job an hour later, not while it is still running.
What pure water costs to run
There are two ways to get it. Buying it ready made from a filling network such as Spotless Water runs at roughly 4.3p a litre plus VAT, which is a few pounds across a normal working day. Making it yourself means a reverse osmosis and deionisation system, typically £1,800 to £4,000 or more for a full van setup, after which the cost per litre drops but you carry filters, resin, electricity and some wastage during purification.
Either way it is a real cost per house, which is worth knowing when you see a quote that looks impossibly cheap.
Questions people actually ask
Can you drink pure water?
Yes, it is not toxic, but it is not meant as your everyday drinking water. With the minerals removed it contributes none of the calcium or magnesium tap water provides, and health bodies do not recommend demineralised water as a sole long term supply. A glass will not hurt you.
Does pure water cleaning work in winter?
Yes. It only stops for hard frost, when water freezes on the glass, and for high winds where working a long pole is not safe. Light rain makes no difference at all, because there is no detergent on the glass for rain to react with.
Why are my windows left wet?
Because the finish comes from the water drying, not from being wiped. There is nothing dissolved in it to leave a mark, so it dries clear. Wiping it would put a cloth's worth of dirt back on.
Do you clean the frames as well?
Every visit. Glass, frames, sills and doors are standard, which is the part that keeps a house looking cared for. The brush and the pure water do the frames at the same time as the glass.
Is it safe for leaded or older glass?
Yes. There are no chemicals involved and no pressure, just a soft brush and water. Around Ironbridge and the older parts of Wellington we work on plenty of period glass this way.
We run pure water across Telford, Wellington, Dawley, Madeley, Ironbridge, Priorslee, Muxton, Shifnal and Newport. If you want to see the difference on your own glass, the instant price calculator takes about thirty seconds.