What adoption actually isAgreement
A pipe built to the right standard with no agreement behind it stays private.
Adoption is a water company agreeing to take a private sewer or lateral drain into its own ownership and maintain it from then on. It is done by agreement with the sewerage undertaker under the Water Industry Act 1991, and the undertaker’s terms set out what has to be designed, built, inspected, tested and recorded before it will take the pipe on.
Two things follow from that. The first is that adoption is decided on paper: the undertaker is being asked to accept a maintenance liability for the life of the asset, and it accepts it on the strength of the drawings and the records, not on anyone’s word that the job was done well. The second is that nothing is adopted until the agreement is completed and the undertaker confirms it in writing.
Before the drawings: the point of connectionEnquiry
Before a drawing is worth starting, the point of connection has to be settled: where the undertaker will accept the flow, at what level, into which system, and whether foul and surface water have to be kept separate all the way. That answer sets the fixed invert the whole design hangs from, exactly as it does on a private run.
The same enquiry establishes whether the receiving sewer has capacity, whether a surface water discharge will be accepted at all, and what rate it will be restricted to. A design drawn before those answers arrive is usually drawn twice.
The drawing set, and agreeing with itselfDrawings
The set is four documents, and each is asked a different question.
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Sheet 1
Layout plan
The line of the pipe against the plot boundaries, the easement, the levels and the point of connection.
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Sheet 2
Long sections
One per run, carrying the figures: ground, cover and invert levels, chainage, diameter and gradient.
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Sheet 3
Manhole schedule
Every chamber by reference: cover level, inverts in and out, depth, internal size, cover class, material.
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Sheet 4
Construction details
How each chamber, bedding arrangement and connection is actually built, drawn once and referred to.
What catches a submission out is disagreement between those sheets rather than a mistake on any one of them. An invert on the schedule that does not match the long section, a gradient on the plan that does not match the chainage and the fall, a chamber shown at one size on the detail and another in the schedule — each has to be reconciled before the set goes in, because the checker will reconcile them anyway.
The calculations behind the pipe sizesHydraulics
The calculations show that each run carries the flow it will be asked to carry at the gradient and diameter drawn, with the foul flow worked up from the units served and the surface water worked up from the areas drained and the rainfall assumed. Where discharge is restricted, the attenuation volume is calculated and the control device is specified with it.
What goes in at completionCompletion
Construction is inspected in stages rather than at the end, because most of what the undertaker needs to see gets buried. The records built up along the way are what completes the submission.
| Point of connection | The undertaker’s answer on where, at what level and into which system. Settled first. |
|---|---|
| Drawing set | Layout, long sections, manhole schedule, details — all agreeing with one another. |
| Calculations | Foul and surface water flows, gradients, attenuation volume, discharge rate, with every assumption stated. |
| Land and easements | Ownership of the land the pipe crosses, the easement width, and the maintenance strip kept clear. |
| Inspection records | Bedding, jointing and backfill signed off at the stages agreed, with dates and run references. |
| Test records | Air or water test, deformation test and infiltration check per run, each on a dated sheet. |
| Post-construction CCTV | Every adopted run surveyed and coded after backfill, with the footage and the log. |
| As-built drawings | The set corrected to what is actually in the ground, including anything moved on site. |
Where a run is built across land that will change hands, the easement and the maintenance strip are settled before the pipe is laid, not afterwards. A sewer the undertaker cannot get a machine to is a sewer it has good reason to refuse.