How Montea will optimize rainwater reuse in their patrimony


Montea is a developing investor in logistics real estate , active in Belgium, France and The Netherlands. They build when requested, but also buy logistics warehouses and rent them out. Montea invests in sustainability in their buildings, of which water is an important factor. Water Experts was contacted to find a solution for some of their challenges related to rainwater reuse, to ensure that it is implemented in an optimal way.


Montea is a well-known developing investor in logistics real estate, that pays a lot of attention to sustainability. At the majority of their Belgian sites, rainwater is collected, stored and reused for toilet flushing. Some of these systems, however, needed to be reviewed and optimized to function properly. Water Experts is performing water audits on several Montea buildings to review the rainwater use and optimize the reuse system. As a result, more rainwater will be reused as the reuse systems don’t fail as often.

The challenge

At several buildings, rainwater is captured from the building roofs and is stored in buffer tanks, ready for reuse. The reuse systems consist of a submersible pump, filters to remove suspended particles, sometimes an activated carbon filter for colour and odour removal and is then distributed to the toilets.

At some locations, the tenants changed from rainwater to tap water because the reuse system didn’t function properly.

Water Experts performs water audits of the buildings in order make it possible to switch again to reusing rainwater instead of tap water. Although some things might seem straight forward, each case is different and should be evaluated carefully to select the best solutions.

The Solution

Firstly, the potential of rainwater reuse is compared to the actual rainwater reuse (monitored with water meters), to check whether the rainwater buffer is dimensioned correctly and to check whether rainwater is reused optimally. Rainwater reuse can be simulated by Water Experts with data from the past years to ensure that the variability of rainfall is taken into account.

The rainwater reuse systems are studied in detail to detect opportunities to optimize them.
Several aspects are evaluated:

The rainwater buffer could be too polluted, which is solvable by cleaning the tank
The inflow in the rainwater tank could lack a preliminary filter to remove bigger dirt particles from the roof, which aims to protect the tank
The inflow in the rainwater tank could be wrongly designed, resulting in the upwelling of the settled solids, which in turn can be pumped to the filter installation and result in clogging
The filter system could be unsuitable, rendering more frequent clogging and, thus, no rainwater reuse
The submersible pump could be installed without floating suction and on the bottom of the rainwater buffer tank, which means settled solids are continuously pumped up and sent to the filter systems.
Tap water addition could be installed in such a way that tap water is injected in the rainwater tank.

This is not optimal for the case when rainwater is depleted, as tap water is added to the rainwater tank in high volumes. When it rains the day after, there could be an overflow to the sewer or infiltration tank, rendering unnecessary loss of tap water
Water meters could be malfunctioning.

To optimize these challenges, several actions can be defined depending on the case-specific needs:

The rainwater tank can be cleaned, potentially once per year
A filter can be installed at the inflow of the rainwater tank (screen, lava filter,…).
This already removes big particles from the water so they don’t end up in the rainwater tan
The inflow design can be as such that it prevents upwelling. This ensures that the settled solids remain in the bottom
The submersible pump should be installed with a floating suction to prevent the pumping of solids on the bottom or at the surface

Tap water addition in case rainwater is not sufficient, should be added in a small buffer vessel in, for example, the technical room.
This is often combined with the distribution pump, that has a small buffer vessel in the pump where tap water is added when necessary. This prevents excess use of tap water addition
The filter system can be monitored based on pressure, to intervene and replace the filter timely and prevent clogging.
Filters with automatic backwash are available as well, to postpone total clogging. This, however, comes with a small water loss for backwashing
The filter system should be designed correctly to ensure proper filtering and prevent frequent clogging. Many types of filters are available for this
The water meters can be checked and monitored online.
This allows to adequately keep track of rain- and tap water use for reporting purposes and to continuously optimize your water use
Potential water savings can be scanned in the building, for example water saving aerators for the taps, or two flush volumes with limited water use for toilets.

The result

Water Experts performs the water audits and reports the findings and recommendations in detail.

The close collaboration with Montea results in a swift acquisition of information, a clear and efficient planning of the actions and a proper follow up of the implementation and information exchange.

The proposed measures can be assessed economically with several technology providers to ensure the best quality and price.

The execution of the measures can be monitored by Water Experts to secure proper installation and functioning after installation.
This approach unburdens Montea and guarantees a solution that is revised by our experts and will result in more sustainable water management.

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