Key principles
"The water calculator within the Code for Sustainable Homes is a fundamentally flawed approach to driving water efficiency in the home. The problems arising from this method are becoming increasingly apparent as more homes are built to the CSH" Marcus Zipperlen, Centre for Alternative Technology
As an ‘appliance based standard’, the AECB Water Standard avoids many of the pitfalls of the Code for Sustainable Homeswhole house calculation method and encourages the uptake of properly functional user-friendly appliances and fittings that are robust and energy and water efficient. The AECB Water Standard has also resolved vital issues relating to plumbing system design and hot water use - thereby robustly addressing the energy impacts of water in the home. Another key difference between the AECB standard and CSH, is that the AECB standard does not encourage rainwater and greywater recycling systems, owing to their higher cost and environmental impact compared to mains.
The AECB standards are based on performance requirements for individual water-using devices rather than a whole building calculation method The calculation method tends to encourage purely notional gains from fittings which can be unacceptable in practice. As many of these fittings can easily be changed, they are likely to be retrofitted with high use fittings, thereby losing most of the potential for water saving. The whole building calculation approach also allows cold-water savings to off-set increased hot water use.
For practitioners familiar with the Code for Sustainable Homes(CSH) water requirements, the AECB standards might seem to be less ambitious. This is in part because the AECB standards do not encourage water recycling and also because acceptable performance is considered, which sets a lower limit on tap and shower flows and bath sizes. Thus whilst an enthusiast might choose to fit a very low flow shower head or a spray tap in the bathroom, most users would find such fittings unacceptable and would almost certainly replace them, perhaps with a very high flow rate fitting. Instead the AECB standards follow the North American and Australian lead by requiring fittings of the lowest water use that have been shown to be acceptable to the majority of users. This does not prevent householders installing even lower flow fittings should they wish to, but this cannot be made a requirement for a building of unknown occupancy.
The AECB Water Standard is available as a free download from: www.aecb.net