Short answer
Before you bid on land, freeze a layout or book pre-app, check whether foul capacity, surface water risk or LLFA rules will force a drainage strategy. A drainage strategy is the document that explains how an English development site will manage foul drainage and surface water in a way the council, the Lead Local Flood Authority (LLFA) and the receiving water company can accept. Get this wrong and validation slips, the LLFA objects, or a foul-capacity abnormal lands after you have already paid for layouts and legal work.
PF & Co produces a desktop planning drainage strategy within Site Appraisal (from £199), and a fuller version inside the Pre-Application Pack (from £1,995). Turnaround is 48 hours from confirmed boundary and brief.
Order a Site Appraisal, or see a sample report first.
When a drainage strategy is triggered
A drainage strategy moves from optional to expected when one or more of the following apply:
- Major applications (10+ dwellings or 1,000+ sqm) trigger the LLFA's statutory consultee role on surface water. A proportionate strategy is expected.
- Critical drainage areas defined in the LPA's Strategic Flood Risk Assessment require a strategy at any scale.
- Rural and edge-of-settlement sites where mains foul capacity is uncertain need an early read on the receiving Wastewater Treatment Works (WwTW) before layouts are fixed.
- Notified capacity constraints from the water company create a known foul abnormal that must be priced and resolved.
- Infiltration-only SuDS sites require infiltration evidence to anchor the SuDS hierarchy: infiltration, attenuation, discharge to watercourse, then sewer as last resort.
- Local List validation requirements that explicitly demand a drainage strategy at submission.
NPPF policy on flood risk and drainage, supported by the Planning Practice Guidance, sits behind these triggers. The sequential test for flood is set out at NPPF paragraph 174 (December 2024). See the GOV.UK flood risk assessment guidance for planning for the wider framework.
The LLFA is the statutory consultee on surface water for major applications and runs its own pre-application process, separate from the LPA pre-app. On rural sites where mains capacity is finite, foul drainage is a common reason schemes stall late. The desktop screen flags where published water company capacity statements show headroom or constraint, and where they are silent, names the capacity confirmation request needed.
What our desktop drainage strategy covers
| In our desktop drainage layer | Sourced from |
|---|---|
| Foul drainage route screening | Receiving WwTW and sewer-asset mapping where published |
| Foul capacity flag | Water company capacity statements where published |
| SuDS hierarchy assessment | BGS infiltration potential and LPA SuDS policy |
| Surface water flood-risk overlay | EA Risk of Flooding from Surface Water |
| Critical drainage area screening | LPA SFRA and Local Plan drainage policy |
| LLFA pre-application triggers | LLFA pre-app process and thresholds |
| Existing site surface coverage analysis | Aerial imagery and OS MasterMap |
| Greenfield run-off rate baseline | LLFA standard methodology where published |
What you receive in 48 hours:
- RAG risk rating across foul, surface water and SuDS feasibility.
- Annotated constraints map with red-line boundary overlay.
- Foul route note naming the receiving WwTW and capacity status.
- SuDS route recommendation against the hierarchy.
- LLFA trigger note: whether a strategy and pre-app submission are required.
- Next-study list with indicative cost range and timeline.
- Drainage abnormal cost allowance for your bid model.
For a 12-unit edge-of-settlement parcel, this typically settles whether the foul route is gravity to an existing rising main, or whether a pumping station and capacity confirmation will sit on the abnormals schedule. That single answer often decides whether the bid stays alive.
For sites with overlapping fluvial or tidal risk, pair this with a desktop flood risk assessment.
What this desktop drainage strategy does not replace
The desktop layer does not include, and does not substitute for:
- BRE 365 infiltration testing. Triggered when infiltration is the proposed SuDS route. Requires intrusive ground investigation.
- Hydraulic modelling of the proposed drainage system by a chartered drainage engineer. Triggered at detailed design.
- Engineer-signed detailed drainage layout under PI. Triggered for technical approval and discharge of conditions.
- Water company sewer-asset confirmation and capacity response. A separate workstream with the receiving undertaker.
- Formal LLFA written response or pre-application outcome.
- Topographical survey for levels and gradients.
- Section 104 adoption agreement under the Water Industry Act 1991.
Where any of these are triggered, the report names the specialist study, indicative cost range and typical timeline.
Four packs sized to four decisions
| Pack | What it does for drainage | Decision moment | Price |
|---|---|---|---|
| Site Appraisal | Foul capacity, surface water risk, SuDS hierarchy, LLFA trigger | Bid or pre-screening | From £199, 48 hours |
| Feasibility Intelligence | Adds drainage abnormal cost provision | Pre-acquisition or pre-architect | From £895, 48 hours |
| Pre-Application Pack | Adds desktop planning drainage strategy for LLFA pre-app | Pre-app meeting booked | From £1,995, 48 hours |
| Planning Intelligence Pack | Tailored drainage strategy alongside chartered engineer sign-off where commissioned | Application submission | Tailored |
If you are pre-bid or in an option agreement, start with Site Appraisal. If pre-app is booked or your architect is ready to freeze the layout, use the Pre-Application Pack.
Send the boundary today
Send postcode, red-line boundary (PDF, KML, GeoJSON or shapefile all accepted), intended use and indicative dwelling count. A chartered planner reviews the brief and the desktop layers are compiled within 48 hours.
You receive: the constraint screen, foul drainage flag, surface water risk, SuDS hierarchy recommendation, LLFA trigger note, next-study list and abnormal cost allowance, ready to drop into your bid model or pre-app brief.
£199 to walk away from a foul-capacity-constrained site before legal and architect spend. £895 to put the drainage abnormal into the bid. £1,995 to walk into pre-app with the strategy ready.
Order a Site Appraisal or see a sample report. For wider planning context, see GOV.UK planning permission guidance.