Practitioners Of Sustainability

The Economics of Green Water

Average Water Consumption per person = 150litres per day.

This is equivalent to about 55m3 (or tonnes) per year.

A 6 person household therefore uses about 350m3/ year.

40% of this is used for toilet flushing and garden irrigation.

Grow

Water is gradually becoming a resource requiring ever greater conservation measures to protect. Hence the recycling of relatively clean ‘wash water’ (grey water) for other, lower grade purposes is important.

The award winning Green Roof Water Recycling System, GROW, developed by AWS is ideal for new build or refurbishment schemes of low-rise multi-story housing and, therefore, particularly suited to the requirements of Local Authorities, Housing Associations and other high density development where significant numbers of residential units are  accommodated in a single block under one roof.

GROW is essentially a constructed wetland arranged as a tiered garden of low growing, flowering, native plants, whose roots can perform the same cleansing function as a reed bed.

Grey water (used wash water collected from showers, sinks and baths) is treated as it flows through the plants’ root system. The treated water is termed green water, which is safe to use for toilet flushing, cleansing public areas, and watering the garden.

  • GROW is a modular system measuring 4m x 2m x 1m (high) and can recycle the wash water of between 30-45 people. It can cut water bills to residents by 30%
  • Larger populations can be served by plumbing more than one GROW unit in parallel.
  • It is very suitable for installation in areas where water is scarce or expensive, especially , for example, in the Mediterranean Basin, island communities or small blocks of flats in urban areas. GROW systems are currently also being researched in the Czech Republic, Pakistan and India.

Price can be negotiated, but allow around €120-180 per person (based on 40 people).

GROW 2, (its baby sister) measures about 2m x 1m x 1m (high) and is suitable for installation on individual properties to produce green water for garden watering and simple horticultural irrigation. (Followthis link for more information about GROW 2)

Beat the next drought and hose pipe bans!

Both GROW and GROW 2 are living systems and require care and simple maintenance to function effectively.

Other Advantages of the Green Roof Water Recycling System:

  • Visual amenity
  • Absorption of dust particles
  • Low maintenance
  • Lower water bills
  • Green credentials for developers and planners

Installed as a single unit at roof top level, this system will require no extra land or valuable basement space, something that makes some other external forms of water recycling a more expensive option, especially in inner cities. The system would also be able to provide thermal insulation to buildings in winter and act as a cooling layer in summer.

In 2002 the DTI awarded GROW a grant under its Partners in Innovation (Pii) scheme to carry out further research using a live source of grey water. GROW was installed at the School of Water Sciences at Cranfield University where it successfully treated the grey water from a block of student flats.

Both GROW & GROW 2 are patented systems.

Opening Day for the GROW installation at The Office Group, Gray’s Inn Road, London

For more information on Green Roofs see greenroofs.org

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