The "Zero PPM" Myth in the Building Cleaning Industry

In glass and solar panel cleaning, there is often debate over the correct conductivity level for the water used. One camp swears by “0 PPM,” while the other is satisfied with values close to zero and, for example, ensures that the purified water used for glass cleaning is below 15 PPM and that water used for solar panel and facade cleaning is below 30 PPM.

As the manufacturer of OSMOBIL systems, we have relied for over 15 years on RO systems that do not use a resin system and therefore cannot achieve zero PPM. Our high-pressure membranes come close to zero PPM (even with very hard water), but do not reach zero PPM. As a result, our units are smaller, more affordable to purchase and maintain, and can remain unused for up to 3 months (since there is no resin, the residual water in the system does not spoil as quickly, and disinfection is not necessary).

Why do we do it this way, and why are we successful with this approach?

So who’s right here? What’s better for cleaning? How many PPM are still acceptable, and how many are no longer acceptable?

In addition to 15 years of practical experience—which tells us that 95% of stains in pure water cleaning are due to user error and are rarely caused by “bad water”—there are hard scientific facts that clearly show: zero PPM is neither necessary nor, in practice, possible. This is probably new to most readers of this post.

Let’s go through this in detail and explore the question:

Why don’t we need zero PPM for osmosis cleaning of windows, solar panels, and metal facades, and why is it sufficient to “get close to zero PPM”?

1. 5 PPM does not equal 5 PPM
For one thing, PPM is a quantitative measurement method and simply tells you, “There is a conductivity value, or there is a particle.” Furthermore, the conductivity in water is not caused by the dissolved minerals themselves, but by the ions they release. And here’s the thing: Not all ions produce the same level of conductivity. That’s why water with a relatively low sodium (salt) content can produce just as high a conductivity level as significantly harder water with a higher calcium and magnesium (lime) content. This also explains why there are water qualities—such as 13 PPM—that leave tiny spots after drying, while others, at 90 PPM, yield perfect results.

2. When do you change the filter?

Even zero-PPM enthusiasts don’t replace their resin filter when the reading jumps from 0 to 1 PPM, but rather at 10, 5, or 15 PPM—and thus operate well beyond the zero mark for a long time.

3. There is no such thing as “zero current”:

A conductivity value of zero PPM is always an interpretation and cannot be physically measured. Zero PPM means: no current. This simply does not exist in the environment. Added to this are various sources of interference, magnetic fields, minute manufacturing tolerances in measuring probes, and many other factors. Consequently, the simple and inexpensive measuring devices we use outside of laboratories have a high standard deviation of 1–4 PPM, even though they are often calibrated.

Residues in the measuring vessel, on the measuring probe, or—for example—simply the CO2 in the air influence the measured value more than, say, the actual residual ions in the water.

6. Flow patterns and water temperature:

The flow pattern over the measuring probe (if it is permanently installed) and the water or ambient temperature have a massive impact on the result. Water temperature, for example, has been proven to affect conductivity: For every degree the water temperature rises, conductivity increases by 2%. For every degree it drops, conductivity decreases. Currently, the water temperature here is 15 degrees. Six weeks ago, it was 9 degrees. That’s a 12% difference. In other words, 5 PPM becomes almost 6 PPM. While good measuring devices compensate for this, deviations can still occur in this regard.

Conclusion: Yes, we need to get down to zero ppm. However, it doesn’t matter whether we’re working with 0, 5, 15, or 20 ppm.