You may have seen a window cleaner working from the pavement with a long blue pole, spraying a façade generously, then leaving without wiping anything. It looks careless. It is in fact a precise method, once you know what is in water.
The problem is not the water, it is the minerals
When a window washed with tap water dries in the open air, it leaves whitish marks. Those are not leftover dirt: they are the minerals dissolved in the water — calcium, magnesium, various salts — left behind on the glass when the water evaporates. Exactly the same deposit as the white film in a kettle.
That is why traditional cleaning requires wiping or squeegeeing: the water must be removed before it dries.
What reverse osmosis does
Tap water is pushed through a reverse osmosis membrane that holds back the great majority of dissolved minerals, then usually passes through a deionising resin that captures what remains. The result is pure, or osmosis, water — almost free of dissolved matter.
That water has a useful property: containing almost nothing, it tends to dissolve what it meets. It lifts dirt from glass more effectively than ordinary water. And crucially, when it dries it leaves nothing behind, because there is nothing to leave.
Hence the method: brush the glazing with pure water, rinse generously with pure water, and let it dry. No wiping, no squeegee, and in most cases no detergent.
The water-fed pole
Pure water is carried through a hose to a pole, usually carbon fibre, ending in a brush and jets. The operator works from the ground.
That is the real benefit: reaching high glazing without ladder, platform or scaffold. Manufacturers offer poles in a wide range of lengths, up to reaches in the order of twenty metres for the longest models — bearing in mind that the longer the pole, the heavier, more flexible and more wind-sensitive it becomes.
In practice there is a height beyond which the pole stops being the right answer — not because it will not reach, but because control of the stroke and reading of the result become insufficient.
What the method does very well
- High glazing reachable from the ground, with no lifting equipment
- Large, regular glazed surfaces
- Façades where placing a ladder would be dangerous or impossible
- Working without chemicals, useful near planting, terraces or sensitive areas
- Regular visits on an already-maintained building
What the method does not do
- Remove baked-on deposits. Old limescale, cement, paint, silicone, adhesive residue: pure water does not dissolve them.
- Repair etched glass. Glazing whose surface has been attacked stays dull, whatever the water.
- Work without thorough rinsing. Insufficient rinsing leaves remobilised dirt to dry in place. The result depends on care, not on the equipment being magic.
- Always suit interiors. Run-off and air drying sit badly with a furnished room. Traditional squeegee work is often better there.
- Ignore wind. A long pole becomes hard to control and the jets disperse.
- Always suffice in one pass. On glazing neglected for years, a traditional reset clean may be needed first.
Judging the result
Let it dry completely before you look. Glass cleaned with pure water looks streaked while wet and becomes clear once dry. Judge in diffuse light, face on, not in raking backlight.
If marks remain after full drying, they usually indicate incomplete rinsing or a deposit that never fell within this method — and that is worth discussing.
How we use it
We choose the method to suit the job, not the other way round: pure water and pole where height and layout allow, traditional cleaning where it is better suited, particularly indoors or on heavily soiled glazing. The chosen method and its limits are stated in the quote.
FAQ
Why don't you wipe after rinsing? Because the water used contains virtually no minerals. As it dries it deposits nothing. Wiping would only put fibres back on the glass.
Is pure water better than glass cleaner? It is different. Very effective on everyday soiling and at height; it does not replace a local treatment on a baked-on deposit.
Any risk to plants or the terrace? Pure water contains no detergent, which is an advantage near planting. Run-off still needs anticipating.