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Does water efficiency lead to dry drains?
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The recent publication of Revised Part G of the Building Regulations has raised, once more, the vexed question of ‘dry drains’. Will reducing the water flow through our drainage system automatically lead to problems arising with solids transport?
Speaking at the AGM of the Bathroom Manufacturers Association, Emeritus Professor John Swaffield, of Heriot Watt University, Edinburgh, thinks not.
After thirty years of research into the issue Swaffield believes that although individual new homes will be required by law to show economies in water usage ( a maximum of 125 litres person per day will be allowed) the overall flow through our drainage system will remain and his personal belief, based on the data which he presented at the AGM, is that dry drains will not become a problem.
“The concept that dry drains could result as a consequence of water conservation has little basis in fact” suggested Swaffield. “Some people are prepared to argue that reductions in WC flush volume should be resisted on the basis that these water saving measures will reduce the flow in the drains, causing blockages. I think that is a myth.”
Part of his presentation concentrated on product design – WCs and drainage pipes.
WC design has progressed steadily over the last 130 years. In those early days toilets were flushed with around 15 litres. Today the legal maximum is 6 litres but innovative manufacturers are designing pans which work perfectly at 4 litres. ( Examples can be found at the BMA’s Water Efficient Product Labelling Scheme www.water-efficiency.org.uk/ )
Swaffield went further and showed an example of a standard wash down WC which had been designed in the 1970s flushing solids successfully with 3 litres.
On drainage design he said that the way forward was with pipes having an egg-shaped cross section. This concept is not new but the shape ( with the point at the bottom ) assists flow by creating a greater depth of water to carry solids. Developers of new homes and builders involved in major refurbishment work may wish to consider the use of such pipework.
The audience at the AGM consisted of bathroom industry leaders and they listened intently to what Swaffield had to say. However, some remained sceptical since, in their view, putting theory into practice had yet to prove conclusive.

Further Information
For further information please email info@bathroom-association.org.uk or
telephone 01782 747123 and visit www.bathroom-association.org

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