What Is Pure Water Window Cleaning, and Is It Really Chemical-Free?
Updated: 5 hours ago
If you have watched a modern window cleaner at work, you may have wondered where the bucket and squeegee went. More and more exterior glass is cleaned with a long pole, a soft brush and what looks like plain water. It is plain water, with one important difference: almost everything dissolved in it has been taken out.
The short answer
Tap water leaves spots because of the minerals dissolved in it.
Pure water systems filter those minerals out on site.
Purified water, a soft brush and a good rinse clean the glass and frames, and the glass dries clear on its own.
No detergent is used on the exterior, so nothing soapy runs into your garden.
Why tap water leaves spots
All tap water carries dissolved minerals. The U.S. Geological Survey describes water hardness as the amount of dissolved calcium and magnesium in the water, and gives a familiar example: glasses that come out of the dishwasher with spots or a film on them.
The same thing happens on a window. When a drop of tap water evaporates, the water leaves and the minerals stay. Water professionals measure this as total dissolved solids, or TDS. The EPA's secondary drinking water standards list TDS among the things that cause deposits and staining, with a guideline of 500 milligrams per liter. Water well under that guideline is perfectly good to drink and will still spot glass.
How the water is purified
A pure water system connects to an ordinary outdoor spigot and passes the water through a series of filters. Typical stages are a sediment or carbon filter, a reverse osmosis membrane and a deionizing resin that removes what is left. Window cleaners check the result with a TDS meter and aim for a reading at or near zero.
Andy uses a Xero pure water system. It travels with him, and it filters your water in your driveway.
How it cleans without soap
Two things do the cleaning. The first is the brush. Soft bristles on the end of the pole scrub the glass and the frame and loosen the dirt. The second is the water itself. Water with nothing dissolved in it readily takes up dirt and minerals, which is why it lifts grime well and why it should not be left sitting on delicate surfaces for long.
After scrubbing, the window is rinsed from the top down and left wet. With no minerals in the water, there is nothing to leave a spot. People are often surprised that the glass is not squeegeed. It does not need to be.
Is it really chemical-free?
This is worth being precise about, because the phrase gets used loosely.
On exterior glass we use purified water only. No detergent, no ammonia, no additives.
Strictly speaking, water is a chemical, so nothing is chemical-free. What people mean is no cleaning products, and that is accurate.
Problem stains are different. Hard water deposits and oxidation need a specific product to remove. If your glass needs that, Andy will tell you first.
Interior glass is cleaned by hand with traditional tools, because you cannot run water down the inside of a house.
Is it better for the environment?
The honest answer is that it avoids some things. No detergent is rinsed onto lawns, plantings or into storm drains. The run-off is water. The process does use water, and filters and resin have to be replaced, so it is not impact-free. For most homeowners the practical benefit is simpler: nothing harsh touches the plants under the windows.
The safety advantage
The pole reaches upper floors from the ground, so most houses can be cleaned without a ladder. That matters. The CDC has reported that 43% of fatal falls over a decade involved a ladder. The International Window Cleaning Association trains its members on the method through a water-fed pole safety module.
Does it work on very dirty windows?
Yes, with more scrubbing and more rinsing. Windows that have not been cleaned for years sometimes need a second pass. What pure water will not do is remove things that are bonded to the glass, such as paint, cement splatter, heavy mineral scale or oxidation. Those need separate treatment, described on our oxidation removal page.
Common questions
Why are my windows left wet?
Because they dry clear. Wiping them would only add lint and streaks.
Does it clean the frames too?
Yes. The brush washes the frame and sill along with the glass, which a squeegee does not do.
My house is on a well. Does that matter?
No. The water is filtered before it is used. Hard well water simply uses up the filters a little faster.
See it for yourself
Our pure water method page has a video of the process. To have your own windows done, request a free estimate.
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