Sustainable drainage systems

In April 2020 we introduced an incentive for Sustainable drainage systems. Full details can be found in our 2020/2021 charges scheme but the information is detailed below:

For measured non-household customers, where it is demonstrated that surface water from an area equivalent to at least 10% of the site is drained to a public sewer via an appropriately designed, built and maintained sustainable drainage system, a reduction will be applied to the chargeable area for surface water charges.

Qualifying systems are determined by us and have been assessed with regard to the Construction Industry Research and Information Association (CIRIA) C753, The SuDS Manual.

 Qualifying sustainable drainage systems

  • Green roof
  • Infiltration system
  • Bio-retention system
  • Detention basin
  • Ponds & wetlands          

In order to qualify for the reduction in the chargeable area, you must apply using the appropriate market form, and include:

  • Drawing to show connectivity, including areas drained via the sustainable drainage system; and
  • As built drawings, to confirm that the system has been designed in accordance with the CIRIA SuDS Manual, with evidence of flow control devices if appropriate; and
  • A copy of the maintenance schedule, with proof of maintenance being completed in accordance with the schedule (e.g. invoice) for a minimum of 12 months
  • A reduction in chargeable area of 80% will apply to the area of the site drained via the sustainable drainage system. The new surface water band is allocated based on the applicable chargeable area for surface water drainage.

We reserve the right to request evidence of effective maintenance of a sustainable drainage system periodically. Where this is not provided, the reduction to chargeable area will be removed.

Where a qualifying sustainable drainage system is installed the reduction will be applied from the date of the change up to a maximum of 12 months from receipt of claim.

A reduction in surface water drainage charges for sustainable drainage is only applied to those customers who pay for this service based on site area.

No adjustment to the chargeable area will be made for highway drainage charges.

  • Additional Guidance

    We will not deviate from the above requirements and only progress the application and any allowance once all relevant documentation has been provided.  

    Any system that does NOT drain to our sewer but for example goes directly to a water course is still considered a full claim and we would not make any charge for this, it will come under the current connectivity claim and follow current process (site visit to check we need to be sure which one the retailer is asking for or they may incur a large fee unnecessarily).  Allowances for full claims go back up to a maximum of 6 years and we do not need to see any maintenance for these systems.

    Where an area is grassed cultivated or landscaped but connected to our network we make a charge, this may now qualify for the reduction (SW Only) if they can provide the relevant information and prove that this is a Sustainable Drainage system.

    On occasion there may be some systems where the surface water goes into our network then into a SUDs system. If it goes into our network BEFORE it enters the SUDs then full charges still apply, as the incentive is for slowing down the surface water getting to our system so that it doesn’t arrive with peak flows of rainfall.

Rainwater Harvesting

More information on our incentive for rainwater harvesting systems.

Find out more