A vegetated rooftop recycling system has been developed that allows water to be used twice before it is flushed into the communal waste water system.
The Green Roof Water Recycling System (GROW) uses semi-aquatic plants to treat waste washing water, which can then be reused for activities such as flushing the toilet.
GROW is the brainchild of Chris Shirley-Smith, whose company Water Works UK is collaborating with Imperial College London and Cranfield University. The researchers are funded by the Engineering and Physical Sciences Research Council.
So-called grey water from washbasins, baths and showers is pumped up to the GROW system, which is constructed on the roof of an office or housing block. It consists of an inclined framework of interconnected horizontal troughs. Planted in these troughs are rows of specially chosen plants that gently cleanse the grey water. Trickling through the GROW framework, the plants' roots naturally take up the dissolved pollutants, leaving 'green water'. Green water is not drinkable and will be dyed with a vegetable colour to signify this, but it can be used to flush toilets or water the garden.

GROWing the next generation of water recycling plants