The Draft National Policy Statement on Waste Water

Supplementary written evidence from the Environment Agency (WWnps 08a)

For some years Building Regulations have required that for most new developments a foul-only sewer is provided and surface water runoff is managed as sustainably as possible; discharge to a sewer being the last resort if other more sustainable options have been shown not to be feasible. Once the Flood and Water Management Act 2010 is implemented this approach will be further strengthened, by requiring surface water drainage to be approved by the Sustainable Drainage Systems (SuDS) approving body, usually unitary and county councils, as meeting SuDS National Standards before construction can commence. Once constructed, the approving body will be under a duty to adopt and maintain those SuDS, which serve more than one property.

Retrofitting sustainable surface water management infrastructure to heavily urbanised areas is enormously challenging. In redevelopment, when surface water discharge to a combined sewer proves the only current feasible option for the portion of the flow that cannot be infiltrated locally, drainage can be separated to foul pipes and surface water pipes with discharge of both pipes to the combined sewer. Should a separate surface water discharge destination become available in future, the surface water discharge from the redevelopment can be connected to it. This is provided for in the Water Industry Act section 116 and Building Regulations Approved Doc H. Re-direction as a mechanism has rarely, if ever, been used. To date there has been insufficient incentive for the sewerage undertaker or developer to cease the surface water connection to the combined sewer and direct the surface water to an alternative destination. One of the challenges will be to deal with any misconnections to the surface system, prior to directing to a surface water sewer or SuDS.

The changes to law in the Floods and Water Management Act 2010, when implemented, should ensure that when surface water sewer connections are made the impact on the capacity in the receiving combined sewer is limited such that, overflows from the combined sewer will not increase excessively or cause an overall deterioration of water quality, or increase in fluvial flood risk elsewhere.

Pressures such as population growth, climate change increases in rainfall, necessarily tight environmental standards, unacceptable risk of sewer flooding, and reducing the greenhouse gas emissions from pumping and treatment, now combine to encourage the removal of surface water sewer discharges that are currently made into combined sewers. The Environment Agency is leading a Defra sponsored Research Project into assessing the costs and benefits of SuDS retrofit. We expect this to follow the 'Paying for Ecosystem Services' approach advocated by the Defra Natural Value Programme. We are also supporting another Defra project led by Ciria providing guidance on how, what and where to retrofit SuDS.

February 2011