TDS stands for Total Dissolved Solids. In window cleaning, it is a way of describing how much dissolved mineral content is present in water. The lower the dissolved mineral content, the less residue the water is likely to leave behind as it dries.
This matters in pure-water window cleaning because the final rinse is designed to dry naturally on the glass rather than being removed with a squeegee.
What does TDS mean?
TDS means Total Dissolved Solids. These dissolved solids can include minerals and salts that are present in ordinary mains water.
A handheld TDS meter gives a reading in parts per million, usually shown as ppm. In practical window-cleaning terms, the reading is used as a quick indication of how much dissolved material remains in the water.
Why can ordinary tap water leave spots?
When ordinary tap water dries, the water itself evaporates but dissolved minerals can remain on the surface. Depending on the water and the glass, that residue can appear as marks or spotting.
That is one reason pure-water systems are used for exterior window cleaning. Reducing the dissolved mineral content means there is less material left behind when the rinse water evaporates.
How is water purified for window cleaning?
Pure-water window-cleaning systems commonly use water-treatment stages such as reverse osmosis and deionisation. The exact system can vary, but the aim is the same: remove dissolved material before the water reaches the glass.
- Reverse osmosis (RO) removes a large proportion of dissolved material through a membrane.
- Deionisation (DI) uses resin to remove remaining charged dissolved ions.
- TDS testing helps the operator check the quality of the treated water.
Does a low TDS reading guarantee perfect results?
No. Water quality is important, but it is only one part of the cleaning process.
Good results also depend on loosening surface dirt effectively and rinsing it away thoroughly. Existing hard-water deposits, paint, silicone, cement residue or other bonded marks are different from normal surface dirt and may not disappear simply because purified water is used.
If you have ever noticed marks after a clean, our guide to spots after window cleaning explains the difference between drying residue and marks already present on the glass.
What happens during a water-fed pole clean?
- The exterior glass is agitated with the water-fed pole brush.
- Loose dirt is lifted from the surface.
- The glass is rinsed with purified water.
- The rinse water is left to dry naturally.
This is why customers sometimes see wet glass immediately after cleaning. That is normal with the method, as explained in our guide to why windows are left wet after cleaning.
TDS and pure water: a simple comparison
| Water type | Dissolved mineral content | What can happen as it dries? |
|---|---|---|
| Ordinary mains water | Contains dissolved minerals | Mineral residue may remain on the glass |
| Purified water | Much lower dissolved mineral content | Designed to dry with far less mineral residue |
Why does TDS matter to a homeowner?
You do not need to understand water chemistry to book a window clean. The useful point is simple: purified water is used so the final rinse can be left on the exterior glass to dry naturally without relying on a squeegee.
For homeowners in Telford, this is part of the same water-fed pole approach used for our residential exterior window cleaning.
What a TDS reading can — and cannot — tell you
A TDS reading is useful, but it should not be treated as a complete diagnosis of a window-cleaning result.
- It can indicate: whether the water contains a higher or lower level of dissolved material.
- It can help check: whether purified water is still being produced as expected.
- It cannot identify: the exact minerals or substances dissolved in the water.
- It cannot prove: that every remaining mark on the glass was caused by the rinse water.
A homeowner’s quick check if you notice marks after cleaning
If you notice a mark after the glass has dried, it helps to separate a possible drying issue from an existing deposit.
- Wait until the glass has fully dried before judging the result.
- Look at whether the mark is a light spot, a fixed chalky deposit or another bonded mark.
- Check whether the same mark was visible before the clean, if you know.
- If you are unsure, take a clear photo and ask the cleaner rather than scrubbing the glass immediately.
This simple check can prevent an old hard-water mark or bonded residue being mistaken for fresh spotting from the cleaning process.
What should you do if you are unsure about the result?
You do not need to measure TDS yourself. If you have a question after a clean, use a simple process:
- Let the exterior glass dry naturally first.
- Check whether the mark looks like loose spotting or a fixed deposit.
- Take a clear photo in daylight if the mark remains.
- Send the photo with the window location when you contact the cleaner.
- Avoid aggressive scraping or chemicals until the mark has been identified.
For Window Cleaning Telford customers, the quickest next step is to send a photo on WhatsApp so the mark can be discussed before any further action is taken.
Frequently asked questions
Is TDS the same as dirt?
No. TDS refers to dissolved material in the water itself. Visible dirt on a window is a separate issue and still needs to be physically loosened and rinsed away.
Can a TDS meter tell exactly what is dissolved in the water?
No. A TDS meter gives a general reading of dissolved material; it does not identify each individual mineral or substance.
Does pure water mean chemicals are always unnecessary?
Not every type of contamination behaves the same way. Normal exterior dirt can often be handled with the water-fed pole process, while bonded deposits may need a different approach. It is better to assess the mark than assume one method removes everything.
Why is the glass left to dry naturally?
The final rinse uses purified water with very low dissolved mineral content, so it can normally be left to evaporate rather than being manually dried. You can read more in our pure-water window cleaning guide.
Window cleaning in Telford
Window Cleaning Telford provides residential exterior window cleaning using a pure-water, water-fed pole method. Regular six-weekly cleaning and one-off cleaning are available.
You can see our current prices or contact us. WhatsApp is the preferred way to enquire.
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