Rainwater harvesting: Millennium Green case study

Gusto Construction Ltd, completed a development site of 24 houses in 1999. Each property on the Millennium Green site was built to a standard far beyond the building regulations and achieved the status of Eco-Excellent. Each property was fitted with a Freerain rainwater harvesting system to meet the water reduction targets. Most of the plots were fitted with a 3,500 litre or a 4,700 litre storage tank, depending on the size of the plot. The system uses a submersible pump to deliver the stored rainwater directly in to the property, without the need for a header tank. The resulting water is suitable for WC flusing, washing machines and outside tap functions. The water is not suitable for drinking or bathing, as this water is non-potable (sometimes called reclaimed or even greywater).

During the year 2001, the Environment Agency and Severn Trent Water carried out a study on one of the plots at Millennium Green to see the progress of the rainwater harvesting system (sometimes called rainwater recycling). They looked at various aspects, including reliability, water quality and amount of mains water was displaced. The weather pattern for the year was not unusal and certainly could be considered an average year.



The above image (available on the main title link in a larger form) shows the level of water in the storage tank day by day. This showed that on a few ocasions a few litres of mains water was added to the storage tank. This is very beneficial as mains water has certain chemicals in it, and the free chlorine does help to maintain the freshness of the water.

Also several times during the year the tank overflowed, which a well designed rainwater harvesting system should do. This allows for any scum layer and suspended particles to be washed. With the Freerain system, the pre-tank filter is housed in the neck of the tank, this allows for the overflowing water to back-wash the filter. Thus reducing maintenance and maintaining water quality.


The study also monitored the amount of water used in the property and the above figure shows the daily percentage split between mains water (in blue) and the rainwater (in grey). The split was almost 50% of each. So when considering the Code for Sustainable Homes you can see that a reduction in mainswater consumption of 50% would mean that per person per day the average usage would drop from 150 litres to 75 litres. An article written on behalf on the Good Homes Alliance suggests that the resulting homeowners might no wish to purchase houses that have the perception of lowering living standards, with water saving device and smaller baths. But the Gusto experience shows that with a typical house and a typical family using water quite freely, a rainwater harvesting system can meet very high standards. All this without comprimising on the lifestyle.