Surface water sewer capacity and the undertaker's position
The right to connect under section 106 of the Water Industry Act 1991 survives, subject to limited refusal grounds. Why the capacity enquiry has to come before the layout is fixed.
Surface water sewer capacity is the item that most often changes a layout after planning permission, and the reason is sequencing. The discharge rate the sewerage undertaker will accept determines the attenuation volume, the attenuation volume determines how much of the site is given over to storage, and the undertaker's answer usually arrives weeks after the drawings were issued.
Make the capacity enquiry before the layout is fixed. The right to connect exists, and it is a right subject to conditions rather than an open door.
Making a capacity enquiry
Every sewerage undertaker runs a developer services function that handles pre-development enquiries. The enquiry is usually a paid service and the response gives you four things: the asset records showing public sewers in and around the site, a proposed point of connection, a statement on available capacity, and any conditions the undertaker would attach.
Submit it with the information the undertaker needs to answer properly. A site boundary plan, the proposed number of units or floorspace, the expected foul flow, the impermeable area before and after development, and your proposed discharge rate and point of connection if you have one in mind.
Ask three questions explicitly, because the standard response does not always cover them. Whether the receiving sewer is combined, foul or separate surface water. Whether the undertaker has a known capacity constraint or a history of flooding downstream. And what discharge rate it would accept, with the basis for that figure.
Do the ground investigation at the same time. If infiltration works, the sewer question may not arise at all, and soakaway testing to the recognised method takes a site visit rather than a programme.
What the undertaker can and cannot refuse
Section 106 of the Water Industry Act 1991 gives the owner or occupier of premises the right to connect drains and private sewers to the public sewer, on notice to the undertaker.
The undertaker may refuse on limited grounds: that the mode of construction or the condition of the drain or sewer does not meet its standards, or that making the connection would be prejudicial to the sewerage system. Notice of refusal has to be given within 21 days of the connection notice, and there is a route of challenge to the magistrates' court.
That second ground, prejudice to the system, is the one that does the work. It is also why outright refusals are uncommon and conditions are standard. An undertaker faced with a surface water connection that would worsen downstream flooding is more likely to agree a point of connection with a restricted rate than to refuse and defend an appeal.
Two points often misunderstood. The right to connect surface water drainage from new development survives, because Schedule 3 to the Flood and Water Management Act 2010, which would have made connection conditional on approval of a drainage system, has not been brought into force in England. And the right to connect is not a right to connect at the most convenient point. The undertaker determines the point of connection.
Restricted discharge rates as a condition of connection
A restricted rate is the normal outcome, and the figure comes from two directions that have to be reconciled.
The lead local flood authority, as statutory consultee on surface water drainage for major development, will set an expectation based on national and local standards: greenfield runoff rate for a greenfield site, and a betterment against the existing rate for a brownfield one. The level of betterment is set locally.
The undertaker sets its own figure based on the capacity of the receiving sewer. Where the two differ, the lower applies, and where the undertaker's figure is the lower one, the attenuation volume rises accordingly.
The discharge hierarchy in national policy and the non-statutory technical standards is what justifies going to a sewer at all. Infiltration to ground first, then discharge to a surface water body, then a surface water sewer, then a combined sewer as a last resort. A drainage strategy that goes straight to the combined sewer without showing why the earlier options fail gets an objection from the flood authority before the undertaker has even replied.
The control structure matters as much as the rate. A hydro-brake or orifice sized for 2 litres per second has to be modelled for blockage as well as for design flow, and the approach set out in the note on modelling a partially blocked flow control is what a reviewer looks for.
Requisitioning a new sewer
Where no sewer of adequate capacity exists within a workable distance, section 98 of the Water Industry Act 1991 allows an owner or occupier to requisition one. The undertaker then has a duty to provide it, subject to the financial conditions in section 99.
Those conditions are where the arithmetic bites. The requisitioner undertakes to meet the relevant deficit, which is the shortfall between the undertaker's costs of providing and maintaining the sewer and the revenue it will receive over a defined period, and security for the sum is normally required up front.
Requisition is slower and more expensive than connecting to an existing sewer, and it is sometimes the only route for a site beyond the edge of the network. Three alternatives are worth testing first: a longer private connection to a sewer with capacity, an off-site diversion under section 185 paid for by the developer, or a package treatment plant with a discharge permit where the site is remote from the network altogether.
Where you build sewers within the site that you want the undertaker to take over, that is an adoption agreement under section 104, and the design has to follow the current design and construction guidance from the outset. Retrofitting an adoptable standard onto a privately designed network after construction rarely works.
Timescales and charges
Build four periods into the programme: the pre-development enquiry response, the formal connection application, any requisition or diversion agreement, and the adoption agreement if one is needed.
Charges come in several forms. The enquiry fee. Infrastructure charges per connection, which undertakers publish annually in their charging arrangements under the regulator's rules. The connection or inspection fee. And the costs of any requisition, diversion or adoption. Take the figures from the current published arrangements rather than from a previous scheme, because they are revised each year.
The commonest programme failure is treating the connection as a construction-stage item. By then the attenuation has been built to a rate the undertaker has not agreed, and the fix is a redesign.
Evidence for the planning application
The Drainage Strategy is where this lands, and it needs the following to survive consultation.
- The discharge hierarchy worked through in order, with the reason each higher option was discounted, and infiltration testing results where ground conditions were considered.
- The existing and proposed impermeable areas, with the calculation of existing and proposed runoff rates and the rainfall dataset identified, as discussed in the note on which rainfall dataset to cite in a drainage calculation.
- The undertaker's written response, appended in full, with the point of connection and the agreed or indicated discharge rate.
- Attenuation volumes for the design events, with climate change and urban creep allowances applied and stated.
- The flow control device, its size and its blockage scenario.
- The exceedance route for events beyond the design standard, drawn on a plan.
- A maintenance and adoption position for every element, saying who owns and maintains what.
Foul drainage is a separate question with its own capacity constraint, and in a catchment with treatment works at capacity it can be the binding one. A Foul Sewage Assessment addresses that, and the two documents should use the same point of connection and the same correspondence.
Note: expect a condition requiring details of surface water drainage to be approved before development starts, and expect the undertaker to be consulted on the discharge. A condition drafted around a rate the undertaker has not agreed is a condition you will be applying to vary.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. To see which flood and drainage documents your site needs, enter your postcode on PlanScope. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Can a water company refuse a surface water connection?
Only on limited grounds under section 106 of the Water Industry Act 1991: that the construction or condition of the drain does not meet its standards, or that the connection would be prejudicial to the sewerage system. Notice of refusal must be given within 21 days and can be challenged in the magistrates' court. Conditions are far more common than refusals.
Is there still an automatic right to connect surface water?
Yes in England, because Schedule 3 to the Flood and Water Management Act 2010, which would have made connection conditional on approval of the drainage system, has not been brought into force. The right is subject to the statutory refusal grounds, and the undertaker still determines the point of connection rather than the applicant.
Who sets the discharge rate?
Two bodies. The lead local flood authority, as statutory consultee on surface water for major development, sets an expectation based on greenfield rates or a betterment on brownfield. The undertaker sets its own figure from the receiving sewer's capacity. Where they differ, the lower applies, and the attenuation volume follows from it.
What is a sewer requisition?
Where no sewer of adequate capacity is within reach, section 98 of the Water Industry Act 1991 obliges the undertaker to provide one on requisition, subject to the financial conditions in section 99. The requisitioner meets the relevant deficit between the undertaker's costs and its revenue over a defined period, usually with security required up front.
When should the capacity enquiry be made?
Before the layout is fixed. The accepted discharge rate determines the attenuation volume, which determines how much of the site is given to storage. Treating the connection as a construction-stage item means building attenuation to a rate the undertaker has not agreed, and the remedy is a redesign.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.