We always strive to meet and exceed the wishes and demands of our clients when developing a Building Maintenance Unit (BMU). This results in incredibly innovative and unique machines being created by our skilled engineering team and installed on the most iconic structures all over the world. In this article, we want to discuss a special feature that can be installed on BMUs and significantly reduces the time for window cleaners to clean a glass facade: a reverse osmosis system. Before we provide an answer to that question, we will first explain what Osmosis is.


Osmosis is a process where a solution (in this case water) that is less concentrated (with salt and other particles) has the natural tendency to migrate to a solution with a higher concentration, when separated by a semi-permeable membrane (figure 1). A semi-permeable membrane is basically a filter that allows certain atoms to pass, while others are stopped by it.

Reverse Osmosis

To clarify this some more: if you would place two tanks of water next to each other (one with a low concentration of salt and one with a high concentration of salt), separated by a semi-permeable membrane, the less salty water would start to migrate to the salty water tank.

As the name suggests, Reverse Osmosis (RO) is the opposite of osmosis: migrating concentrated water to less concentrated water through a membrane. Because this is not a natural process, energy is needed to force the concentrated water through the membrane.

As can be seen in figure 2, pressure is applied, forcing the concentrated water through the semi-permeable membrane. When water travels through the membrane, it filters out salts, organics, bacteria and other contaminants.

This process removes up to 99% of the contaminants in the water!

Why Use Reverse Osmosis water?

For window cleaners, Reverse Osmosis water has multiple advantages that ease and speed up the work when compared to using ‘normal’ water.

The most important advantage is that RO-water is residue-free, meaning that the surface dries spot-free and no squeegee or sponge is needed. This saves valuable time for the window cleaners, as they only have to brush the window with a water-fed pole and rinse it by pulling back the brush. Because less actions are needed, cleaning a window may be done up to 50% faster! Also, the surface stays clean for a longer period of time. Because window washers work faster and the frequency of cleaning windows is lower when RO-water is used, the costs for window cleaning are reduced significantly.

Another advantage is that no chemicals or cleaning products are needed. The purer the water is, the more aggressive it gets. RO-water breaks the bond between the dirt and the window on ionic level, making it easy to rinse the dirt off, making this an environmental friendly way of cleaning as well. Also in high-rise construction, architects and contractors strive to work as environmental friendly as possible. Reverse Osmosis perfectly fits this trend.

You can imagine that the characteristics of RO-water are of great value, economically as well as environmentally, when a large surface needs to be cleaned regularly. Like the glass facade of a skyscraper for example.

Reverse Osmosis System on a BMU

A BMU to access a skyscraper’s facade for maintenance purposes and an RO-system is a perfect combination for window cleaners to do their work fast and effective. But, the challenge is to combine the two systems from a design-perspective. Facadexs has designed and manufactured multiple BMU’s that are equipped with an RO-system.

To facilitate work with RO-water, a RO-installation has to be placed near the location where a BMU will be operating. Among other things, you need a high-pressure pump, several water tanks, a motor driven electric reel and a high-pressure water hose. The system will purify the water and after that, it’s transported to the BMU. One of the installations Facadexs installed on a BMU, can process up to 600 liters of water (158 gal.) per hour.

BMU adaptations

A BMU needs to be customized to facilitate window cleaning with RO-water. The hose with pure water needs to be guided along the jib to the gondola, where the workers use a water-fed pole to clean the windows.

The most striking difference with ‘standard BMUs’ is the reel to guide the hose. Imagine that this hose can be hundreds of meters long to be able to reach the lower parts of the facade. The electric powered reel is operated by the workers to adjust the hose’s length.

After the reel, the hose travels along the jib to the spreader. This spreader is equipped with a guiding wheel to guide the hose downwards, to the gondola.

The gondola is also customized to enable workers to work safely with a water-fed pole: to prevent that the hose is subject too much tensile pressure, because it’s too short, an overload protector is installed in the gondola. This way, the workers are warned and can adjust the length of the hose. Furthermore, a system is installed to work with a water-fed pole.

Custom made BMU’s by Facadexs

BMUs equipped with a Reverse Osmosis system are the perfect example our innovativeness and our mission to ease the maintenance of facades for our clients all over the world. Reverse osmosis is still gaining popularity among window cleaners and clients, as they are becoming aware of its advantages in terms of labor time, environmental friendliness and the savings that can be made with it. Especially when it concerns large cleaning surfaces of tall buildings.

Curious about how we can support you in terms of facade access and customizing BMUs to get the best solution for your project?