Ordering sewer records and pre-development enquiries

Order an asset location search and a pre-development enquiry from the sewerage undertaker before the layout is fixed, not after. A sewer records pre development enquiry tells you two different things: where the public assets are, and whether the network has capacity to take your foul and surface water. The first is a plan. The second is a commercial and technical answer that can take weeks and that occasionally changes the scheme.

Undertakers keep records of public sewers, disposal mains and lateral drains under the Water Industry Act 1991, and they publish those records to developers as a paid search. What they do not do is guarantee that the records are complete or that the positions shown are accurate.

Ordering the search

Go to the undertaker for the area, which is the sewerage undertaker rather than the water supplier where those differ. Most publish a developer services portal with an asset location search, sometimes called a sewer records search or a map of public sewers.

You will normally need a site plan with a red line boundary, an ordnance survey based plan at a stated scale, and a fee. Turnaround is usually a few working days for the records themselves.

Order the search at the same time as the topographical survey. Overlaying the two is the exercise that matters, and doing it early costs nothing while doing it late costs a redesign.

Reading the records and their accuracy

Records typically show the line of each public sewer, manhole positions with reference numbers, pipe diameter, material where known, direction of flow, and sometimes invert levels and cover levels.

Every set comes with a disclaimer, and the disclaimer is accurate. Positions are approximate, historic records were transcribed from paper, and depths are frequently indicative. Treat the plan as a strong indication of where to dig trial holes, not as a survey.

There is a particular issue with assets that transferred to public ownership in October 2011, when many formerly private sewers and lateral drains in England and Wales became the undertaker's responsibility. Many of those were never surveyed, so they are public assets that may not appear on the records at all. On an infill plot in an older suburb, assume something is there until a survey says otherwise.

Commission a drainage survey with manhole lifts and, where the layout depends on it, a closed circuit television survey. It is a modest cost against the risk of finding a 225 mm foul sewer under a plot you have already sold.

Private drains, which do not appear

Records show public assets. A drain serving a single property up to the boundary remains private and will not be mapped.

So on a garden plot or a backland site, the drainage serving the host house is invisible on the search, and it very often crosses exactly where the new foundations are proposed. The same applies to private rising mains, land drainage, and connections that were made without the undertaker's knowledge.

The practical answer is the same as above: lift covers, trace the runs, and check the fall. Where a private drain serves more than one property, check whether it in fact transferred and is now public, because that changes who consents to the works.

The pre-development enquiry

The capacity question is asked through a pre-development enquiry, sometimes called a pre-planning enquiry or a developer enquiry, depending on the undertaker.

You submit the site location, the number and type of units, the estimated foul flow, the proposed surface water strategy and the intended points of connection. The undertaker responds on whether the network can accept the flows, whether reinforcement is needed, and whether any conditions or phasing would apply.

Three things to know about the answer.

Undertakers now routinely refuse surface water connections to a foul or combined sewer where any alternative exists, which reflects the drainage hierarchy in national guidance: infiltration first, then a watercourse, then a sewer.

A capacity constraint is not usually a refusal. It more often means a network reinforcement, funded through the connection charging arrangements, with a programme attached. That programme is what affects your build out.

And the response is normally time limited, so an enquiry answered two years before you submit may need refreshing.

Timescales and the programme

Records come back quickly. Pre-development enquiries take substantially longer, commonly a few weeks, and each undertaker publishes its own service standard.

Build the sequence into the programme in this order: asset location search, drainage survey, pre-development enquiry, then the drainage design. Running the design before the enquiry means designing twice.

Where a connection requires a new sewer to be built and adopted, the adoption agreement process adds months and has its own technical standards, so start it as soon as the layout is stable rather than at the point of construction.

Build over and build near agreements

Building over or within three metres of a public sewer requires the undertaker's agreement. This is a separate consent from planning permission and from building control approval, and planning permission does not authorise it.

The agreement process considers access for maintenance, the depth and condition of the sewer, the foundation design, and whether diversion is a better answer than protection. Common outcomes are a deeper foundation, a reinforced concrete lintel spanning the pipe, a protective slab, or a diversion at the developer's cost.

Where the sewer runs through the middle of the developable area, diversion under the Water Industry Act is the usual route, and it is not quick. Set out the detail alongside the layout rather than leaving it to a condition, and see building over or near a public sewer for how the agreement itself works.

Using the response in the drainage strategy

The undertaker's response is evidence, and it belongs in the application.

A Drainage Strategy that states the point of connection, quotes the undertaker's capacity response with its reference number and date, sets out the surface water hierarchy and why each higher option was discounted, and gives the discharge rate and attenuation volume, answers most of what the lead local flood authority will ask.

Foul drainage gets its own treatment where the site is not connecting to a public sewer or where capacity is constrained, and a Foul Sewage Assessment is the document that covers the calculation of flows, the proposed treatment and the consenting route for any discharge.

Where the site relies on a package treatment plant or a septic tank, the environmental permitting position needs checking as well, because a discharge to ground or to a watercourse is regulated separately from planning.

Order the search this week, book the manhole survey, and send the pre-development enquiry before the architect finalises plot positions. Those three steps in that order remove most drainage risk from a small site. You can also check which supporting reports the application will need while the enquiry is with the undertaker.

This is general guidance, not legal advice. For specialist technical reports, qualified professional input may be required, and undertakers' procedures differ, so check the position with the relevant undertaker 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.