Runoff rainwater is not clean

Rainwater that falls is relatively clean. But once it ends up in the gutter, undesirable and harmful substances from roofs, cars, and streets are washed away with the water.



In a scientific study by Boogaard et al (2014), the concentrations of polluting substances in Dutch runoff rainwater were measured. The measured concentrations of many substances, including nutrients, copper and zinc, exceeded the Dutch standard for maximum allowable concentrations (MAC) for receiving waters. Microplastics are also becoming an increasing source of concern.


Rockflow cleans runoff water from roads and roofs

The natural environment and the quality of life in cities benefit from clean groundwater and surface water. That's why it's good to pre-purify runoff rainwater before it infiltrates into the ground. A buffer from ROCKWOOL Rainwater Systems consists of stone wool. This Rockflow package quickly absorbs the fallen rainwater, preventing urban floodings. And it retains a lot of pollution. Thus, the water that infiltrates into the ground or is discharged into surface water is much cleaner. The stone wool system itself can be cleaned in no time.

Stone wool captures pollution - with the power of stone

Stone wool is made from rock. The mineral fibres of stone are microscopically small. These fine fibres form a dense network with a large surface area, effectively filtering out pollution. Therefore, a Rockflow buffer not only captures water but also cleans it: The fibre structure effectively holds back suspended particles and common dissolved pollutants in urban stormwater. Our field results show an average reduction of 50% of the most common chemical pollutants in the captured run-off water:


Solid particles

Chemical pollutants

This is how Rockflow works as a filter

Stone wool fibre network
The water supply channels in Rockflow systems are easy to inspect and clean.
This can be done time and again using standard sewer cleaning equipment. After cleaning, the system is as good as new.

Eric Gallé


Project in the spotlights: Cleaning 'first flush' on the RijnlandRoute