The Green Roof Water Recycling System (GROW) is a vegetated rooftop recycling system that uses plants to treat waste washing water, which can then be reused for activities such as flushing the toilet.
Water from washbasins, baths and showers is pumped up to the GROW system, on the roof of an office or housing block. On interconnected horizontal troughs specially chosen plants (water mint, yellow flag iris, marsh marigold, and the common reed) cleanse the grey water. Their 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.
The next step is to see if GROW can be reduced in size to sit above a household water butt, for individual households. The team will also investigate whether the addition of an ultraviolet light can enhance the disinfection of the water. They hope to market GROW commercially in the second half of 2006.
By Chris Shirley-Smith, with Imperial College London and Cranfield University.