Section 104 sewer adoption and planning conditions
Sewer adoption under section 104 of the Water Industry Act 1991 follows the undertaker's standards, not the planning condition. How to reconcile the two before discharge.
A section 104 agreement is the contract under which a sewerage undertaker agrees to adopt a new sewer, lateral drain or pumping station once it has been built to the undertaker's standards. It sits in section 104 of the Water Industry Act 1991, and it runs on a track entirely separate from the planning permission. The two tracks have to be reconciled by the developer, because neither the undertaker nor the planning authority will do it for you.
Most of the trouble on a residential site comes from the same place. The planning condition requires a surface water drainage scheme approved by the authority, often on the lead local flood authority's advice, while the undertaker will only adopt assets that meet its own design and construction requirements. Where the two sets of requirements diverge, the developer ends up owning the gap.
What adoption actually gives you
Adoption transfers the asset and its maintenance liability to the undertaker. After the declaration of vesting, the sewer is a public sewer, the undertaker maintains it and the statutory right to connect under section 106 of the 1991 Act applies to it.
Without adoption, the pipes stay private. Somebody has to own them for the lifetime of the development, which means a management company, a service charge and a mechanism in the transfer documents. On a 40-unit scheme that is a long-term administrative cost and a reason purchasers' solicitors raise enquiries.
The adoption process since April 2020 runs under the Code for Adoption Agreements, with sector guidance including design and construction requirements and a model agreement used across the undertakers in England. That replaced the older arrangements and brought a common build standard, a standard application route and standard timescales. It did not make adoption automatic.
Design standards the undertaker applies
The undertaker applies its own technical requirements, and they are not the same as the drainage design the planning authority approved.
Recurring differences include minimum pipe diameters and gradients, manhole spacing and type, cover levels and the depth at which a sewer is acceptable, the position of the asset relative to buildings and trees, and whether the asset can sit under a private driveway or has to lie within an adoptable highway or a dedicated easement. Pumping stations carry the tightest criteria: standby capacity, emergency storage, access for a tanker, screening, odour control and a minimum number of properties served before the undertaker will take one on at all.
Sustainable drainage is the live issue. The current guidance allows adoption of sustainable drainage components in defined circumstances where they function as sewers and meet the design requirements, so a piped conveyance system and some storage structures can be adopted. Open attenuation basins, swales, rain gardens and permeable paving frequently cannot, or can only with a commuted sum, which puts them back into a management company arrangement. Our note on planting specification for swales and wetland margins covers the maintenance regime those features need once somebody has to look after them.
| Asset | Usual adoption position | Who maintains if not adopted |
|---|---|---|
| Gravity foul sewer serving more than one property | Adoptable under a section 104 agreement | Not applicable in practice |
| Surface water sewer to an approved outfall | Adoptable where it meets the design requirements | Management company |
| Foul pumping station | Adoptable where it meets the undertaker's criteria | Management company, with a sinking fund |
| Attenuation basin or swale | Often outside adoption | Management company or, by agreement, the authority |
| Permeable paving on private drives | Not adopted | Individual owners, by covenant |
Where adoption and planning conditions collide
Four conflicts come up repeatedly, and all four are easier to resolve before the application is determined than afterwards.
- Discharge rate. The planning condition fixes a restricted rate, often to greenfield run-off. The undertaker's requirements may dictate a pipe size or a flow control type that does not deliver that rate without an additional chamber the planning drawings do not show.
- Layout. The undertaker needs clear access and standard easements. A layout approved with plots over the sewer line, or with a basin in the position the undertaker wants for a manhole, has to be amended, and that can mean a non-material amendment or a section 73 application.
- Maintenance responsibility. A condition requiring a management and maintenance plan for the lifetime of the development has to name a body. Writing "the water undertaker" before the agreement is signed is a hostage to fortune.
- Phasing. Adoption usually follows a maintenance period after the works are complete, so the asset is still private when the first occupiers move in. A condition tying occupation to adoption is unworkable and should be resisted at the drafting stage.
The resolution is sequencing. Get the undertaker's technical acceptance of the drainage design, in writing, before you ask the authority to discharge the drainage condition. Then submit both to the authority together, with a drawing that reflects what the undertaker has accepted. A Drainage Strategy written with the adoption position already settled is a much shorter document than one written hopefully.
An illustrative example
This example is illustrative. A 55-dwelling site has a planning condition requiring surface water discharge limited to the greenfield rate via a single flow control, with a maintenance plan for the lifetime of the development. The approved layout shows an attenuation basin in a public open space area and a short carrier drain to a watercourse outfall. The undertaker declines to adopt the basin, accepts the carrier drain, and asks for the flow control chamber to be relocated 4 m to give tanker access. The developer agrees a management company for the basin, moves the chamber by a non-material amendment, and submits the undertaker's acceptance letter alongside the condition discharge application. Eight weeks saved compared with discovering the position after the first occupation.
Bonds, inspection and release
A section 104 agreement is secured by a bond or other surety, set as a proportion of the estimated cost of the adoptable works and held until the undertaker is satisfied.
The sequence is agreement, then construction under inspection, then practical completion, then a maintenance period during which the developer remains responsible for defects, then the declaration of vesting and release of the bond. Build the bond cost and its duration into the appraisal, because it is capital tied up for longer than most cash-flow models assume, and a defect found at the end of the maintenance period extends it.
Two practical points. Keep the as-built records and CCTV survey in the form the undertaker specifies, because missing records are the commonest cause of a delayed vesting. And do not let the groundworks contractor deviate from the agreed design without the undertaker's inspector agreeing it on site, because an unapproved change can take the asset outside the agreement.
Keeping the planning drainage case aligned
The planning drainage case and the adoption case should be written from the same hydraulic model and the same drawing set.
That means one set of rainfall inputs, one set of climate change allowances and one agreed outfall. Our note on which rainfall dataset to cite in a drainage calculation explains why the choice matters when two reviewers check the same numbers. Where the outfall is to a watercourse rather than a sewer, the design has to satisfy the riparian and consenting position as well, which we cover in outfall design, bank stability and scour protection.
One wider point worth keeping in view. Schedule 3 to the Flood and Water Management Act 2010, which would create a separate approval route for sustainable drainage with its own adoption duty, has not been brought into force in England. Government has stated an intention to implement it, and the detail will matter for adoption when it happens. Until then, work to the current adoption guidance and check the position before relying on anything else.
Settle the adoption position before the drainage condition is discharged, and write both documents from the same model. Enter your postcode on PlanScope to see which drainage and flood reports your site is likely to need.
This is general guidance, not legal advice. Check the position with your sewerage undertaker, your lead local flood authority or a qualified professional before relying on it. 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 does a section 104 agreement do?
It is an agreement under section 104 of the Water Industry Act 1991 by which a sewerage undertaker agrees to adopt a new sewer, lateral drain or pumping station once it has been built to the undertaker's standards. On vesting, the asset becomes a public sewer and the undertaker takes on its maintenance. Without it, the pipes remain private.
Are sustainable drainage features adopted?
Sometimes. Current sector guidance allows adoption of components that function as sewers and meet the design requirements, so piped conveyance and some storage structures can be adopted. Open basins, swales, rain gardens and permeable paving often fall outside adoption or require a commuted sum, which leaves a management company responsible for them.
When should the adoption application be made?
Before construction of the adoptable assets starts, and ideally before the planning drainage condition is discharged. Obtaining the undertaker's technical acceptance first means the drawing submitted to the authority already reflects what will actually be built, which avoids a later non-material amendment or a section 73 application to move an asset.
Can a planning condition require adoption?
A condition can require a maintenance and management plan naming the responsible body, but a condition tying occupation to adoption is unworkable because vesting normally follows a maintenance period after completion. Resist that drafting at the decision stage, and offer a management arrangement that covers the interim period instead.
Is Schedule 3 to the Flood and Water Management Act 2010 in force?
Not in England. Schedule 3 would create a separate approval route for sustainable drainage with its own adoption duty, and government has stated an intention to implement it. Until it is brought into force, adoption runs under the current sector guidance. Check the position before relying on any announced change.
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.