Circular Rain

With Circular Rain we are investigating an innovative storage, purification and use of rainwater. By buffering and simultaneously purifying harvested rainwater, a variety of useful applications can be envisaged.

Rainwater harvesting is becoming increasingly important. This is partly connected to climate change, which in the Netherlands seems to be causing more frequent peak downpours. But the fact that more and more of the land surface is being built-upon and paved also plays a role, since it means that the rainwater can no longer be discharged through the soil. There are useful applications for harvested rainwater, but the water has to meet quality standards which depend on the specific application.


EWB has developed an innovative filter based on shells and a mineral mixture. The filter can be used to purify the harvested rainwater. Laboratory research will reveal the filter’s effect on the water quality.

A desk study is also being conducted to identify the substances present in harvested rainwater, as well as their concentrations. This will be followed by an investigation of the quality standards that the water must satisfy for several pilots, and what this implies for the requirements that need to be set for a purification method for harvested rainwater.


Column experiments have been carried out in KWR’s lab to determine the purification performance on the rainwater of the shells, the mineral mix and of the combination of the two systems. Based on these results, a measurement programme will be established for the different pilots.


A number of pilots are being run in this project:

  • a study of extinguishing water at BON in Wijster; this pilot is now underway;
  • a study of recreational water in Amsterdam (started in May 2020).

In addition, possible pilots are being explored in Leiden (recreational water and sprinkling water for sports pitches), process water in Den Helder (brewery), and in Wetteren (‘Urban Rainshells’ for allotment gardens and a recreational square). Measurements have also been done on harvested and treated rainwater at sports pitches in Goes, where the EWB system is being used.