Drainage and sewerage management plans in planning terms

A drainage and sewerage management plan is the long-term capacity plan a sewerage undertaker publishes for its network, and it is becoming the document that decides whether a housing scheme can connect now or has to wait. The duty to prepare one sits in section 94A of the Water Industry Act 1991, inserted by the Environment Act 2021, and it requires undertakers to assess the capacity of their drainage and sewerage systems, identify risks and set out how they will manage them over a planning horizon of decades.

For a developer the practical question is narrower. When a water company responds to a consultation saying the network has no headroom until a reinforcement scheme completes in a stated year, where does that statement come from and how much weight does it carry? It comes from this plan, and the answer on weight is: enough to get a condition, rarely enough to get a refusal.

As at October 2026 the statutory framework is in force and undertakers have published plans, with a review cycle of at least every five years. Check the current published plan for the relevant undertaker rather than relying on a summary, because the catchment-level detail is what matters.

What the plans are and who prepares them

Each of the sewerage undertakers in England and Wales prepares a plan covering its area. The industry developed the approach as drainage and wastewater management plans before the statutory duty arrived, which is why both names are in circulation and why older documents use the earlier label.

The plan works down from the company area to drainage catchments and then to individual systems, with a risk assessment for each. What a planning case officer actually sees is the output at system level: whether a treatment works or a sewer catchment is forecast to have capacity for projected growth, and what intervention is planned if it does not.

Statutory basis and cycle

Section 94A sits alongside the undertaker's general duty under section 94 to provide and maintain a system of public sewers. The planning horizon is long, at least 25 years in practice, and the plan has to be reviewed and republished on a cycle of no more than five years.

Two features matter for development. First, the plan covers surface water and foul drainage together, so a growth allocation that looks fine for foul flows can still sit in a system with a surface water problem. Second, the plan is forward-looking and allocates capacity against planned growth in the local plan, which means an unallocated windfall site may not be in the assumptions at all.

How capacity evidence is used in planning

Capacity is awkward in planning terms because of the right to connect. Section 106 of the Water Industry Act 1991 gives an owner or occupier the right to connect drains and sewers to the public sewer, subject to notice and to the undertaker's limited grounds for refusal. An undertaker cannot simply decline a connection because its network is tight.

So capacity shortfalls are managed by conditions rather than refusals. The undertaker's consultation response typically asks for one of three things: a drainage strategy to be approved before works start, a phasing condition tying occupation to the completion of network reinforcement, or confirmation of the connection point and discharge rate.

That is where the plan feeds in. A response that says reinforcement is programmed for a stated year is drawing on the published plan, and an applicant who has read the same document can respond precisely rather than generally.

Consultee responses that rely on them

Sewerage undertakers are consulted on major applications and often comment on minor ones. Their responses have become more specific since the plans were published, and they now routinely cite catchment-level capacity findings.

What to do with such a response:

• Ask for the system reference and the capacity assessment behind the statement
• Check whether the site was in the growth assumptions used for the plan
• Establish whether the constraint is foul, surface water or treatment works headroom, because the solutions differ
• Ask what the undertaker would accept as mitigation: attenuation on site, a restricted discharge rate, a pumped connection to a different system, or phasing

A Foul Sewage Assessment is the right place to record all of this, with the pre-development enquiry response, the capacity position and the agreed connection point set out in one document the case officer can rely on.

Phasing conditions and Grampian wording

Where reinforcement is needed, the condition will usually be Grampian in form: no occupation of more than a stated number of dwellings until specified off-site works have been completed. Such conditions are lawful where there is a reasonable prospect of the works being carried out within the lifetime of the permission, and national guidance on the use of planning conditions sets out the tests they must meet.

Negotiate the wording. Three details decide whether the condition is workable:

1. The trigger. Occupation of a stated number of units is better than commencement of development, because it lets site works and sales progress.
2. The definition of completion. Reference to the undertaker's written confirmation is cleaner than a description of the works.
3. The fallback. A clause allowing an alternative drainage solution agreed in writing avoids a return to committee if the reinforcement programme slips.

Where there is no reasonable prospect of the off-site works at all, the condition fails the tests and the application is in trouble. That is the rare case where a capacity constraint really does defeat a scheme.

Where a scheme must wait for reinforcement

Some catchments have a hard constraint, usually a treatment works at its permitted discharge limit under an environmental permit. The permit, not the pipe, is the binding limit, and it is varied by the Environment Agency on the undertaker's application rather than by the planning system.

Illustrative example. A 90 dwelling scheme on an allocated site where the treatment works has no permitted headroom until an upgrade completes. The planning answer was a condition limiting occupation to 30 dwellings until the undertaker confirmed the upgrade, with an alternative of a temporary package treatment plant if the programme slipped by more than a year. The scheme proceeded and the later phases followed the upgrade. The numbers are illustrative; the structure is the one that works.

Where a private solution is proposed instead, the standards and consents are different again, and the drainage design has to stand on its own merits.

Using the plan in a foul sewage assessment

Quote the plan rather than paraphrasing a consultee. Name the undertaker, the plan, the catchment or system reference, the publication date and the finding you rely on. Then state what the scheme does in response.

The same discipline applies to surface water. A Drainage Strategy that assumes a surface water connection in a catchment the plan identifies as at risk will be queried, and the better position is to design for a greenfield run-off rate with on-site attenuation and treat any sewer connection as a last resort. The approvals landscape here is still moving, and the position on Schedule 3 SuDS approval is worth checking before assuming who signs off the design.

Keep the water supply side in view as well. Where the catchment is also subject to water scarcity or neutrality requirements, a Water Supply Assessment covers ground the drainage plan does not touch. Reform in this area moves quickly, and the planning law timeline is the place to follow it.

This is general guidance, not legal advice; check the position with your local planning 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.