Good practice

Rainwater harvesting in office building

Rainwater harvesting in office building
© Bianca, #250861979, 2019, source:
High cost
Resource savings: Water:
The building requires 400 m³ less water from the water network yearly compared to not having the rainwater harvesting system
Associated cost savings: Water:
Premises and operation areas:
Office building
Advancement in applying resource efficiency measures:

Making the most of a vital resource

  • Opportunity to install a rainwater harvesting system as part of a major office rennovation
  • Rainwater harvesting reduces the need for clean drinking water thus decreasing environmental impact

In 2015 and 2016 an old office building in Limelette, Belgium was renovated. The project included several measures to reduce energy and drinking water consumption. Among these was using rainwater to supply toilets and sinks. The rainwater is collected off the building and stored in a 20 m³ tank on the roof of the building. Around 450 m³ of water can be harvested over the year. This is enough to supply most of the water needs, although there is also a limited supply of drinking water in kitchens, showers, and laboratories. 

During the wetter seasons, the tanks fill up and the overflow is routed to an area where it can be absorbed into the natural groundwater system rather than discharging it to public sewers. This area is located near the entrance alongside information about the water conservation measures.

The rainwater harvesting system is only one component of a comprehensive renovation which cost around € 1.8 million. Installing similar systems in old buildings is often too expensive or impractical to be considered. But when done together with a major renovation including the replacement of water pipes and plumbing, it is feasible.

Key benefits

  • Less demand on fresh water supplies
  • Better capture and use of rainwater
  • Secure water supplies during very hot or drought conditions
  • Rainwater no longer discharged into public sewers
  • Lower environmental impact

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