Combined blue roofs, rainwater & greywater harvesting

How it works

The concept of storing water on a roof may seem crazy, but blue-green roof technologies have proven to be a safe, credible water management solution over the past decade.

Blue-green roofs

Blue-green roofs work by capturing rainwater in hollow storage crates on the roof area of a building. Rainwater is allowed to naturally infiltrate into these crates through a growth medium which is usually partially or totally covered in vegetation.

A flow restrictor safely controls the rate of runoff from the roof, all whilst preventing the roof structure from becoming overloaded.

After passing through the flow restrictor, rainwater would then typically go to the drain. This is a huge waste of a valuable resource, especially when many buildings commonly use drinking water to flush their toilets!

Greywater Recycling

The above water management solutions can even be combined with greywater recycling where large volumes of recycled water are required to meet large demands.

Greywater recycling is the collection and reuse of bathroom wastewater from showers, handwash basins, and bathtubs. Greywater is safely filtered through a natural biological treatment process to remove contaminants.

Both the rainwater and greywater can be used to top up a central header tank.

Will water quality be impacted?

The biggest question we get asked about combining these technologies is about water quality, especially where green roofs are included. Concerns around discolouration and soil debris entering the rainwater supply have traditionally been too much of a risk for specifiers.

In our experience, a good quality blue-green roof and a properly specified water reuse system can handle the increased soil content. We like to compare this system to watering a hanging basket. At first, the water runs out of the hanging basket with clumps of soil. Then, after a short period, the water begins to run clear.