Sewerage design standards and sewer adoption approval
Adoptable sewers are designed to the sewerage undertaker's standards, not the council's. Here is what governs the layout, how the application runs and where the programme slips.
Adoptable sewers are designed to the sewerage undertaker's standards and approved by the undertaker, not by the local planning authority. Two separate approvals run in parallel on any scheme with a shared drainage network: the planning permission with its drainage conditions, and the agreement with the water company that lets the pipes be adopted and connected. Developers lose months by treating the second as something to sort out after the first.
The sequence that works is a pre-development enquiry during site appraisal, a drainage strategy that reflects the capacity answer you get back, then the formal adoption and connection applications once the layout is fixed.
Which standards govern an adoptable sewer
Since 1 April 2020 the position in England has been set by the Sewerage Sector Guidance published for the water companies, which brought in a single Code for Adoption Agreements and the accompanying Design and Construction Guidance. That package replaced the old Sewers for Adoption series, and it applies to every sewerage undertaker in England, so a developer working across regions no longer meets a different document in each one. Wales operates its own version.
The statutory basis sits in the Water Industry Act 1991. Section 104 is the adoption agreement itself, the instrument by which the undertaker agrees to take over a sewer once it is built and tested. Section 106 is the separate right to connect a drain or sewer to the public system. Section 98 lets a developer requisition a public sewer where none exists within a reasonable distance, and section 185 covers diverting an existing one that crosses the site.
These are different applications with different forms and different fees. An adoption agreement does not give you a point of connection, and a connection consent does not make a pipe adoptable.
The design rules that shape a layout
The design criteria matter at masterplanning stage because they decide where roads and plots can go. A few of them reshape layouts more than people expect.
Adoptable foul sewers start at 150mm internal diameter. Gradients are set to achieve a self-cleansing velocity, conventionally taken as 0.75m per second at a defined flow condition, which is why very flat sites end up with pumping stations rather than gravity runs. Manhole spacing is limited so that the run between chambers stays within the reach of standard jetting and inspection equipment, typically no more than about 90m on smaller pipe sizes. Changes of direction and junction arrangements have to happen at a chamber rather than mid-run.
Surface water sewers are designed against a storm return period for the pipe network itself and then checked for exceedance, so a layout needs somewhere for water to go when the design event is exceeded. Overland flow routes, basins and permeable surfaces all take land, and that land has to be shown before the unit count is fixed.
Sewers inside the site also need to be in land the undertaker can reach. Pipes running under private gardens, under buildings or through land the developer will sell off are the most common reason a nearly finished layout has to be redrawn. Keep adoptable runs in highway, in public open space or in dedicated easements of the width the undertaker specifies.
Verify the current numbers against the live Design and Construction Guidance before you draw anything, because the criteria are revised and the undertaker's own addendum can be stricter.
The stages of an application to the undertaker
The process is more predictable than its reputation suggests, provided each stage is treated as a gate rather than a formality.
- Pre-development enquiry. You ask for asset records, a capacity assessment and an indicative point of connection for a stated number of units or a stated discharge rate.
- Technical submission for the section 104 agreement. Full drainage design, calculations, long sections, chamber schedules and a layout showing what will be offered for adoption.
- Agreement and bond. The adoption agreement is executed, a bond or other security is put in place, and the design is locked.
- Section 106 connection application for the actual connection to the public sewer, including the method and the point.
- Construction under inspection, with the undertaker attending at agreed hold points.
- Final inspection, CCTV survey and testing, then vesting of the sewer once the maintenance period ends.
A scheme that also needs a requisition under section 98 or a diversion under section 185 adds a further track, and those tracks are the slow ones because they involve the undertaker designing and building in public highway.
Pre-development enquiry and the capacity answer
The capacity response is the single most useful piece of paper you can hold at acquisition. It tells you whether the existing network can take your foul flows, whether surface water can discharge to a sewer at all, and what the undertaker will insist on by way of restriction.
Read it for three things. First, the point of connection offered, and how far it is from the site boundary. Second, any statement that reinforcement or upgrade works are needed, because that is cost and programme sitting with the undertaker's own delivery timetable. Third, the discharge rate the undertaker will accept for surface water, if it will accept any at all. The hierarchy in national policy and guidance puts infiltration first, then a watercourse, then a sewer, and undertakers increasingly refuse surface water connections where another route exists.
Where no public sewer is within reasonable distance, the scheme falls back on a package treatment plant or a requisition, and that decision belongs in the foul sewage assessment rather than being left to the discharge of conditions. The evidence a council expects in that situation is set out in more detail in what to show where there is no mains sewer.
Points of connection and what they cost you
An offered point of connection is a commercial fact as much as a technical one. A connection 300m off site in adopted highway means a section 50 street works licence, traffic management, reinstatement to the highway authority's specification and a programme that depends on a road space booking rather than on your groundworker.
Where the route crosses third-party land you need an easement, and the landowner knows it. Where it crosses or discharges to an ordinary watercourse you need land drainage consent from the lead local flood authority, which is a separate approval again and is covered in land drainage consent for works to an ordinary watercourse.
Pumping stations deserve their own warning. If the undertaker will only adopt a pumping station built to its standard, the footprint, access track, odour control, power supply, telemetry and standoff distance to the nearest dwelling all have to be designed in. A pumping station discovered late tends to cost a plot or two.
Timescales that move the build programme
Nothing here is quick, and the published target times assume a complete submission.
| Stage | What it depends on |
|---|---|
| Pre-development enquiry | Undertaker's standard response period, counted from a complete enquiry with a site plan and unit numbers |
| Section 104 technical approval | Quality of the calculations and whether the layout keeps sewers in adoptable land |
| Bond and agreement execution | Legal turnaround on both sides, often the quiet delay |
| Section 106 connection consent | Method statement and whether highway works are involved |
| Network reinforcement by the undertaker | The undertaker's own capital programme, which can run to many months |
| Vesting after the maintenance period | CCTV results and remedial works |
Start the pre-development enquiry before you submit the planning application. The capacity answer shapes the drainage strategy you submit, and a strategy that assumes a surface water connection the undertaker has already refused will be picked apart by the lead local flood authority consultee.
Schedule 3 of the Flood and Water Management Act 2010, which would introduce a statutory SuDS approving body and a mandatory standard for new drainage, has still not been brought into force in England as at the time of writing. Government has signalled an intention to implement it. Until it is in force, approval of surface water design continues to run through planning conditions and the undertaker's own requirements, so do not plan a programme around a regime that does not yet exist.
What the planning conditions usually ask for
Councils rarely condition the adoption process directly. They condition the outcome. The wording you tend to see requires a detailed foul and surface water drainage scheme to be submitted and approved before any development begins, with evidence that the receiving network has capacity and that the discharge rate matches what was assessed.
Two practical points follow. A pre-commencement condition of that kind cannot be discharged until the undertaker has given you something in writing, so the capacity response and the point of connection offer become planning documents. And a condition that fixes a discharge rate will bind you even if the undertaker later offers something more generous, so get the number right at application stage rather than arguing it afterwards.
This is general guidance, not legal advice. Check the position with your local planning authority, the sewerage undertaker for the area and a qualified drainage engineer before relying on it.
To see which drainage and utilities documents a site is likely to need, enter your postcode on PlanScope and work through the guided questions. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What replaced Sewers for Adoption in England?
From 1 April 2020 adoptable sewer design in England has been governed by the Sewerage Sector Guidance, which contains a single Code for Adoption Agreements and the Design and Construction Guidance. It applies across all English sewerage undertakers, so the same technical document now covers schemes in different water company regions. Wales runs a separate version.
Is a section 104 agreement the same as a connection consent?
No. Section 104 of the Water Industry Act 1991 is the agreement under which the undertaker will adopt a sewer you build. Section 106 is the separate statutory right to connect a drain or sewer to the public system. You need both on most residential schemes, and holding one does not give you the other.
Can a water company refuse a surface water connection?
Yes. The drainage hierarchy puts infiltration first and a watercourse second, with a public sewer as the last resort, and undertakers do refuse surface water connections where another route is available. Get the position in writing through a pre-development enquiry before the drainage strategy is drafted and submitted.
Why do adoptable sewers have to stay out of private gardens?
Because the undertaker needs permanent access to maintain and replace them. Runs under buildings, through plots that will be sold or across land without an easement of the required width are routinely rejected, which forces a layout redraw. Keep adoptable pipes in highway, public open space or dedicated easements from the first layout.
When should the pre-development enquiry be submitted?
Before the planning application, ideally during site appraisal. The capacity response tells you the point of connection, whether network reinforcement is needed and what discharge rate will be accepted, and all three shape the drainage strategy. Submitting a strategy that contradicts the undertaker's answer invites an objection from the drainage consultee.
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.