Study explores water efficiency impact on drainage

Drainage design standards should be reviewed to keep up with the drive to improve water efficiency - and avoid blocked drains and sewers.

That is the verdict of a report from the Environment Agency following a joint investigation by scientists and water experts.

Less Water to Waste concludes better design and guidance for retrofitting water efficient fixtures and fitting is needed to ensure sewerage systems can work with less water.

It follows a shift towards the use of more water efficient fixture and fittings in homes and offices, such as toilets with use minimal amounts of water to flush.

The Environment Agency expects this to increase as water metering becomes more widespread and the new Building Regulations come into force.

Ian Barker, head of water resources at the Environment Agency, said: "We needed some good quality research into what the impacts of this might be.

"We were particularly interested in assessing the impact of low-flow toilets because reducing flush volume is the most effective way of cutting demand.

"But flushing is vital for shifting sewage through the system."

Fortunately, the report concludes that higher water efficiency standards are unlikely to pose problems for most drains and sewers.

But very low volume toilet flushes could be an issue in a few existing buildings where drains serve a small number of single occupancy properties.

In new properties, the study recommended that drainage design standards are reviewed to accommodate higher levels of water efficiency, perhaps by setting pipes at steeper gradients and using toilets that use air as well as water during the flush.

In existing buildings, the study concludes that drainage layout should be considered before deciding whether to replace an old toilet with a new low-flush model.

Mr Barker said although his team found no reports of blockages caused by water efficiency, further research should be carried out to prevent problems bubbling to the surface in future.

Kate Martin



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