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Dry Drains – myth or reality?
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Dry drains are not an issue. They are not a problem. It’s a myth.
So says John Swaffield, Emeritus Professor at the School of the Built Environment, Heriot Watt University, Edinburgh. He was speaking at the recent AGM of the Bathroom Manufacturers Association in Stoke, giving his very personal view on the perceived problems of ‘drainline carry.’
Prior to the main business of the meeting John Swaffield addressed the capacity audience of bathroom industry leaders and special guests. His technical presentation, which had the audience riveted, addressed the subject of ‘dry drains’ – a concern which had been initiated by pressure groups in the US and had been followed closely in the UK.
Emeritus Professor John Swaffield

“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. Careful appliance design and careful drainage system and pipe design, together with inevitable climate and social changes, will minimise the probability of dry and blocked drains.”
Swaffield went on to explain his thinking. His presentation made a very detailed and considered review of the arguments surrounding drainline carry. He suggested that it was necessary to examine the concept of the dry drain, rationally. Several aspects should therefore be considered and balanced against each other.
On climate change Swaffield examined the latest forecasts suggesting wetter winters and higher summer temperatures. Water availability will become more problematic and water conservation will continue to be a major issue for government, industry and the home owner. There will be pressure to reduce the consumption of water per person so on an individual basis less water will be consumed. But the population is growing so, obviously, total consumption is set to grow.
On social and demographic change he showed the most recent figures regarding the number of households in England. They are projected to grow to 27.8 million in 2031 with one-person households set to increase to 18 per cent of the total population. Single person homes are known to use more water than multiple occupancy homes. The increase in single parent homes and single occupation are bound, therefore, to increase water demand.
On product design, the solution he considered is to improve appliance design so that water conservation “just happens, almost without the user noticing.” WC development has achieved just this over the last 100 years and so is set to continue.
Swaffield suggested that WC design is essential to water conservation. Much work is being carried out today by product manufacturers but they should not lose sight of the fact that there is a wealth of information already available from the last thirty years of research. “We should not be fooled into re-inventing the wheel,” he said. “The findings from that research can be readily accessed but perhaps newcomers feel too inhibited, for some reason, to go and find it. It may also be that those who created the original research feel too inhibited to advertise it.”
Regarding drainage pipes themselves pipe diameter and ovality is important. Smaller diameter pipes and pipes with a cross section similar to an egg are known to improve flow – “provided that the pointed bit is at the bottom!”
Swaffield’s arguments concluded with the thought that reducing WC flush volumes is always the first response to water conservation targets. And quite rightly so since research has shown that reductions in flush volumes can be achieved without exacerbating other drainage problems. Careful drainage design with swept curves, accurate slopes and no top entry should always be used.
In conclusion Swaffield said “Climate change and demographic evidence suggests that, while water conservation will continue to be a priority, water usage levels are much higher than 20 years ago and will continue to be so even if current government targets, in the latest Part G Building Regulations, are achieved. Good design of both WCs and drainage has been proved to mitigate solid deposition. On the basis of this evidence my personal view is that dry drains are a myth.”
Delegates listened intently to what Swaffield had to say and to his solutions to ensure that drains remain clear. However, some delegates remained sceptical since in their view putting theory into practice had yet to prove conclusive. Perhaps the “jury remains out.”
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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Ends
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