If you’ve ever watched a window cleaner wash your windows with a long pole and then walk away without drying them, you might have wondered: Won’t the water leave marks when it dries?
It’s a perfectly reasonable question, especially if you’re used to traditional window cleaning with a bucket, soapy water and a squeegee.
The answer lies in a method called pure-water window cleaning, also known as water-fed pole cleaning or sometimes reach-and-wash.
Although this technology has been around for more than 25 years, many people outside the window cleaning industry aren’t familiar with how it works.
Here’s a closer look at the water we use, how we clean each window and why we deliberately leave the glass wet.
What is pure-water window cleaning?
Pure-water window cleaning uses specially purified water delivered through a telescopic pole fitted with a brush.
Unlike traditional window cleaning, which usually involves applying a cleaning solution and removing it with a squeegee, this method relies on brushing, thorough rinsing and allowing the remaining water to evaporate naturally.
The important difference is the water itself.
Ordinary tap water contains dissolved minerals, including calcium and magnesium. When tap water evaporates, some of these minerals can remain on the surface, leaving spots or visible marks.
Purified water has had almost all of these dissolved minerals removed. When used correctly to rinse a clean window, it can evaporate without leaving mineral deposits behind.
That’s why we don’t need to wipe the glass dry.
Where does the purified water come from?
The water used for professional pure-water window cleaning is quite different from ordinary household tap water.
It goes through a purification process that commonly involves two technologies:
Reverse osmosis (RO)
Water is passed through a very fine membrane that removes a large proportion of its dissolved minerals and other impurities.
Deionisation (DI)
The water then passes through a vessel containing a special ion-exchange resin. This removes remaining dissolved mineral ions, producing water with an extremely low mineral content.
The resulting water is often described in the industry as zero-TDS water. TDS stands for Total Dissolved Solids, and a reading of zero parts per million (PPM) indicates that the amount of dissolved material is below the meter’s detection threshold.
At Window Hero, we obtain our purified water from specialist water-filling stations and store it in a tank in our vehicle, ready to use throughout the day.
Sometimes we add a very small amount of specialist rinse aid to help the water spread and rinse more effectively. This works on a similar principle to the rinse aid used in a dishwasher. It doesn’t replace the purification process.
How we actually clean your windows
There’s more to pure-water window cleaning than simply spraying water onto glass.
The order in which we clean, the way we use the brush and, particularly, the final rinse all contribute to the finished result.
1. We start with the upstairs windows
We normally begin with the highest windows and work our way down the property.
There’s a practical reason for this: water continues to drain from the frames and sills for a short time after cleaning.
By starting upstairs, we allow that water time to drip away before cleaning the windows below. Otherwise, water and debris from an upper window could run onto glass we’ve already cleaned.
2. We wash the window frames first
With purified water flowing through the brush on our water-fed pole, we begin by washing the window frames.
Frames can collect dust, cobwebs and dirt, particularly around their upper edges and corners.
Cleaning the frames first is important. If we cleaned the glass before the frames, dirt from the frames could wash down onto the freshly cleaned glass.
We use the brush to scrub away this build-up while the flowing water helps carry the loosened dirt away.
3. We scrub the glass
Once the frames have been washed, we move onto the glass itself.
We work the brush across the surface, agitating and loosening accumulated dirt, dust and other deposits.
Some marks need a little more attention. Hardened bird droppings, for example, can be difficult to remove immediately.
Rather than repeatedly scrubbing a stubborn deposit, we may soak it with purified water, continue cleaning other windows and return once it has softened.
The purpose of this stage is to loosen and remove the dirt before the final rinse.
4. We clean the window sills
Next, we move down to the sills.
Window sills often collect a considerable amount of dirt, dust and other debris because they’re horizontal surfaces exposed to the weather.
We scrub these areas with the brush and purified water, removing the accumulated dirt.
At this stage, the frames, glass and sills have all been washed. However, some of the water on the glass still contains loosened dirt from the cleaning process.
This is why the next stage is so important.
5. We rinse the glass thoroughly — without touching it
Once the scrubbing is complete, we stop touching the glass with the brush.
We then carry out a final rinse using a continuous flow of purified water.
We start at the very top of the glass, paying particular attention to the upper edge, where water and loosened dirt can sometimes remain trapped around the frame.
From there, we work downwards in overlapping, side-to-side movements, guiding the flow of water across the entire pane.
This downward rinsing action carries away the dirt and residue loosened during scrubbing, along with the water that has collected it.
The aim is to replace the dirty wash water with fresh, highly purified rinse water.
Keeping the brush away from the glass during this final stage also helps prevent loosened dirt on the brush from being transferred back onto the clean surface.
The final rinse is one of the most important parts of the entire process. Even perfectly scrubbed glass can dry with marks if dirty water is allowed to remain on it.
6. We wipe the frames and sills
After rinsing, we finish by wiping down the frames and sills with microfibre cloths.
This removes remaining surface water and helps give these areas a tidy finish.
The glass itself, however, is deliberately left wet.
Why don’t we dry the glass?
This is probably the part of modern window cleaning that surprises people the most.
With traditional window cleaning, a squeegee removes the water before it evaporates. That’s necessary because ordinary water or cleaning solutions can leave deposits behind.
Pure-water cleaning works differently.
After the final rinse, the water remaining on the glass contains very little dissolved mineral matter. As it evaporates, there are no significant mineral deposits to create the familiar water spots.
There’s no need to use a squeegee or wipe the glass with a cloth.
In fact, by the time we’ve finished cleaning the last window on a property, the first windows we cleaned are often already nearly dry.
You can sometimes watch the remaining droplets gradually disappear, leaving clear glass behind.
The key is not simply using purified water, but making sure the final rinse has removed the dirt loosened during washing.
What if the windows dry with marks?
Pure-water window cleaning is effective, but it isn’t automatic. Good technique still matters.
If marks appear after the glass has dried, there are several possible explanations.
Dirt or residue may have remained on the glass because the final rinse was insufficient. Water trapped in dirty window seals or frame joints may also drip onto the glass after cleaning, carrying deposits with it.
Some marks may not be ordinary dirt at all. For example, hard-water staining, paint splashes and certain mineral deposits can remain attached to glass even after routine washing.
So while windows being left wet is completely normal with this method, visible dirt or spotting after they’ve dried shouldn’t simply be dismissed as part of pure-water cleaning.
The finished result, rather than whether the glass was dried by hand, is what matters.
Is pure-water window cleaning better than traditional cleaning?
Both methods can produce excellent results when used correctly.
Traditional window cleaning, using a washer and squeegee, remains particularly useful for interior windows and situations where water needs to be controlled or removed immediately.
Pure-water cleaning is especially practical for exterior windows because telescopic water-fed poles allow cleaners to reach many upstairs windows while remaining on the ground.
It also allows the frames, glass and sills to be washed as part of the same process, without routinely needing detergent on the glass.
Neither method eliminates the need for proper cleaning technique. Removing the dirt thoroughly and leaving a clean surface is what matters.
The simple explanation
Pure-water window cleaning works by combining three things:
- Agitation: The brush loosens dirt from the frames, glass and sills.
- Rinsing: A thorough flow of purified water carries the loosened dirt away.
- Natural drying: The remaining low-mineral water evaporates without leaving the deposits associated with ordinary tap water.
So the next time you see your windows left wet after a clean, there’s no need to be concerned simply because the cleaner hasn’t used a squeegee.
Provided the glass has been properly washed and rinsed, allowing it to dry naturally is exactly how the process is designed to work.