Sewer connection rights and capacity refusals

The right to connect to a public sewer is statutory. Section 106 of the Water Industry Act 1991 entitles the owner or occupier of premises to connect drains and private sewers to the public sewer, and the sewerage undertaker cannot simply refuse because its network is busy. What an undertaker can do, and routinely does, is refuse on the narrow statutory grounds, impose a point and method of connection you did not want, or tell the local planning authority that development should be phased until network improvements are delivered. The planning consequence is a Grampian condition rather than a refusal, and the programme consequence can be years.

The statutory right to connect

Section 106 gives the right, and section 106(4) gives the two grounds for refusal: that the mode of construction or condition of the drain or sewer being connected does not satisfy the undertaker's standards, or that the making of the connection would be prejudicial to the undertaker's sewerage system.

Notice is served on the undertaker, which then has a defined period to object. A refusal has to be justified on one of those grounds, and there is a statutory route to challenge it, so a bare assertion of insufficient capacity should not be accepted at face value.

The practical position differs between foul and surface water. For foul flows, the right is strong and undertakers are expected to accommodate growth by improving the network, which is what their periodic investment cycle is for. For surface water, the answer is usually that you should not be connecting at all: the drainage hierarchy puts infiltration and watercourse discharge ahead of a surface water sewer, and a combined sewer last of all. An undertaker refusing a surface water connection while offering a restricted foul-only connection is applying that hierarchy rather than obstructing you.

Grounds on which an undertaker can refuse

"Prejudicial to the sewerage system" is the ground that carries the arguments. It covers flooding of other properties, breach of the environmental permit at the treatment works, and hydraulic overload of a specific length of sewer.

Three points follow for a developer.

The test is about the system, and not about the undertaker's preference for a later connection date. Where the constraint is at the treatment works rather than in the network, the issue may be the Environment Agency permit, which is a different conversation involving a third party. And where the constraint is a single length of undersized sewer, an offsite improvement funded by you may be cheaper than the delay, which is a commercial calculation to run early.

Nutrient neutrality catchments complicate this further, because the treatment works discharge consent and the habitats assessment interact. That is a separate workstream from the connection itself, and it needs to start before the application, not after.

Capacity assessments and pre-development enquiries

Every large undertaker runs a developer services function with a pre-development enquiry service. Use it before you apply for planning permission, not after.

What to ask for, in writing:

• Confirmation of the public sewer records in the vicinity, with asset plans.
• The proposed point of connection for foul, and for surface water if any.
• A capacity assessment for the flows you have quantified, foul and surface water separately.
• Any network constraint identified, its location, and the scheme and date that would resolve it.
• Whether a drainage impact assessment or hydraulic modelling is required, and to what specification.
• The consenting route and timescale for any offsite works.

Quantify the flows properly before you ask. An enquiry based on a unit count without peak flow calculations produces a generic answer that will not help you at committee. The Foul Sewage Assessment is where those numbers and the undertaker's response belong, and the surface water side sits in the Drainage Strategy.

Requisitioning a new sewer

Where there is no public sewer within a reasonable distance, or the existing one cannot serve you, the Water Industry Act 1991 provides a requisition procedure. The undertaker has a duty to provide a public sewer on requisition, subject to financial conditions: you secure the cost, and the undertaker offsets the future revenue from the connected properties against it over a defined period.

The mechanics matter for cash flow. You are funding an asset the undertaker will own, with a partial rebate mechanism that depends on properties being occupied and paying charges. Get the offer in writing with the payment profile before you commit, and factor the securities the undertaker requires.

Two alternatives are worth testing against a requisition. A section 104 adoption agreement, where you build the sewer to the undertaker's standard and it is adopted on completion, is the usual route for sewers within a development site. And a private pumping station remains an option where gravity connection is impossible, with the caveat that adoption standards for pumping stations are demanding and a station that is not adopted becomes a management company liability in perpetuity.

Timescales and their effect on programme

This is where schemes lose years, and the ranges are wide enough that only the undertaker can give you dates.

A pre-development enquiry response is typically weeks. A hydraulic modelling exercise commissioned by the undertaker is typically months. An offsite network improvement delivered through the undertaker's own investment programme is scheduled against that programme's periods, which is why "capacity will be available following completion of the scheme in the next investment period" is an answer that can mean several years.

Programme accordingly, and ask the question that actually matters: what is the earliest date at which the first dwelling could be occupied, and what would have to happen to bring that forward. A developer-funded improvement, a phasing plan, or a temporary solution with an agreed switchover are the three answers you might get.

Grampian conditions on drainage capacity

A local planning authority faced with a capacity constraint has a choice. Refuse, or grant subject to a condition preventing occupation until the network improvement is complete.

The negative condition, usually called a Grampian condition, is the normal outcome, and national guidance on the use of conditions is clear that such a condition is only appropriate where there are reasonable prospects of the required action being performed. That gives you two things to establish in the submission: that the improvement is programmed or fundable, and that the phasing works commercially.

Draft the condition yourself and offer it. A condition tied to a specified improvement scheme with a defined trigger is manageable. A condition requiring "confirmation from the sewerage undertaker that capacity is available" with no mechanism is a condition you may never discharge, because nobody at the undertaker is responsible for issuing that confirmation.

Watch the wording on occupation as well. "No dwelling shall be occupied until" is workable in phases. "No development shall take place until" stops your groundworks for a reason unconnected with groundworks.

Evidence for the planning submission

The officer and the drainage consultee need to see five things, and they need them in one place.

1. The flows: foul peak flow with the calculation basis, surface water rates existing and proposed, with a climate change allowance.
2. The public sewer records with the proposed connection point marked.
3. The undertaker's written response to the pre-development enquiry, dated, in full rather than quoted selectively.
4. The constraint, if any, with the resolving scheme and its programme.
5. The proposed phasing or condition wording that accommodates it.

Where the site also has surface water risk, keep the drainage capacity argument separate from the flood risk case in the Flood Risk Assessment, because conflating them produces objections from two consultees at once.

Illustrative example: a 60-dwelling site where the undertaker identified a hydraulic constraint 400 m downstream. Options were a developer-funded upsizing of that length, or phasing occupation of the final 22 plots until the undertaker's own scheme completed. The applicant priced both, offered a Grampian condition tied to the specific scheme reference, and consented the upsizing as a fallback. Permission was granted with the phasing condition, and the fallback was never needed.

For single dwellings the analysis is much shorter, and the note on drainage evidence for a single new dwelling covers what is proportionate there.

Enter your postcode on PlanScope to see which drainage and flood documents your site is likely to need.

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.