Using Greywater – a means to an end
30/05/2011 | Using Greywater – a means to an end The requirements of both the Code for Sustainable Homes and Approved Document G of the Building Regulations are encouraging housing developers to consider greywater recycling more than ever before. Yvonne Orgill, CEO of the Bathroom Manufacturers Association, looks at greywater in more detail and considers how it can be used to reduce water consumption and achieve higher Levels in ‘Code Homes.’ One definition of greywater is that it is the wastewater from showers, baths, washbasins, washing machines and kitchen sinks which can be collected and, after basic and minimal treatment, be used for other purposes around the home such as flushing the toilet or watering the garden. These are uses which don’t require perfectly good water of pure drinking quality. Typically, a basic simple domestic system will collect greywater and store it before reusing it to flush the toilet or divert it to the garden. A more complex system treats the greywater to a standard that can be used in washing machines. Systems for flushing the toilet can save around a third of the daily household water demand. A trial by the Environment Agency showed a range of water savings from about 5 per cent to 36 per cent. As newer properties tend to have lower toilet flush consumption, the maximum savings in a new build might be closer to 20 per cent. Problems may sometimes arise when warm, nutrient-rich greywater is stored for a long period. These ideal conditions are perfect for incubating bacteria but there are currently three approaches for dealing with this problem. The first is to limit the time that the greywater is stored. Some systems incorporate a dump valve which empties the storage tank after a set period of inactivity. Another approach is to use chemical disinfectants, such as chlorine compounds, to inhibit bacterial growth. This extends the length of the possible storage time. On a far grander scale, the approach is to treat the greywater in a small dedicated sewage treatment plant. Since it contains little organic matter the treated water runs clear and is free of unpleasant odours. This approach uses a significant amount of energy and is comparatively expensive. The cost-effectiveness of greywater recycling is as variable as the systems themselves. The amount saved will depend on volume of water saved, the price of the mains water it replaced and the cost of installing, running and maintaining the system. More information is available from the BMA’s new ‘eco-zone’ web pages at www.bathroom-association.org/eco-zone