What is a percolation test and why is it required?

A percolation test measures soil infiltration. Results are used to size a drainage field appropriately and are commonly requested by Building Control for new or replacement off-mains systems.

What are General Binding Rules (GBR)?

General Binding Rules set conditions for small sewage discharges. Where they apply, systems must meet siting, operation and discharge limits; some sites still require permits or alternative solutions.

Section 106 refers to legal permission to connect to a public sewer. An application to the sewerage undertaker is typically required before making a new connection.

What is Section 104 adoption?

Section 104 is an agreement for a sewer to be constructed to adoptable standards so that, once completed and inspected, the sewer can be adopted and maintained by the water company.

Do I always need Building Control approval?

Many drainage works, especially new or replacement off-mains systems and significant alterations, involve Building Control. Expect to provide design notes, percolation results, and completion evidence.

Drainage Compliance & Regulations – Plain-English Guide

Neutral guidance on permissions, standards, and evidence: Building Control, General Binding Rules, Section 106 sewer connections, Section 104 adoption, percolation tests, and discharge routes.

Need a quick sense-check? Ask DrainageGPT about your specific plan (new soakaway, tank replacement, sewer connection). You'll get a plain-English checklist.

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Big picture: what "compliant" usually means

Right solution for the site: soil, space, groundwater, and proximity to watercourses/wells.
Right approvals: Building Control, sewer connection consent (Section 106) where relevant, and any discharge permissions.
Right evidence: percolation test (where a drainage field is proposed), drawings, design notes, commissioning/servicing records.
Right operation: routine emptying/servicing, and keeping fats/wipes/chemicals out of the system.

Building Control (what they typically expect)

Design intent: what you're installing/replacing and why.
Percolation results & sizing: required where a drainage field is proposed.
Layout drawings: location of tanks/fields, separation distances, ventilation, access for emptying.
Commissioning & completion evidence: records, photos, and test results as applicable.

Ask in chat for a simple submission checklist tailored to a septic tank, treatment plant, or soakaway upgrade.

General Binding Rules (GBR) & small discharges

Small on-site sewage systems are often subject to conditions on siting, discharge quality, maintenance, and where discharges can go. Some locations or flows fall outside the rules and need a permit, consent, or an alternative design.

What this usually means for homeowners

Direct outfalls to ditches/streams may be restricted without compliant treatment and consent.
Evidence of maintenance, desludging, and correct operation is expected.
Upgrades/replacements are assessed on current standards, not historic practices.

Percolation testing (core for drainage fields)

A percolation test determines whether the soil can accept treated effluent and how large the drainage field needs to be. Without testing, designs tend to fail early (undersized) or be wasteful (oversized). Building Control commonly expects recorded test data and calculations with the application.

Not sure where to dig test pits or how many to run? Ask in chat for a step-by-step outline.

Section 106 (new sewer connections)

Section 106 is the process for securing permission to connect a private drain to the public sewer. Applications normally include drawings, flow details, and method statements. You'll need to coordinate timing, traffic management (if in the street), and inspections.

What to prepare

Site plan and proposed route/connection point
Method statement and reinstatement details
Evidence that private works are watertight and constructed correctly

Thinking of replacing a septic tank with a mains connection? The septic tanks page explains how this ties into compliance and what alternatives exist.

Section 104 (adoption of new sewers)

Section 104 covers agreements to build new sewers to adoptable standards so the water company can take ownership after completion. While more common on developments, small private schemes that intend future adoption follow the same principles: agreed specifications, inspections, and a maintenance period before final adoption.

Discharge routes & permissions (plain-English)

To a watercourse: normally requires a consent route and meeting quality/flow conditions.
To ground (drainage field): requires suitable soil (proven by percolation testing) and proper sizing.
Surface water vs foul: must be kept separate unless a specific design/consent states otherwise.

Documentation you'll be glad you kept

Percolation test records and design calcs
Drawings/"as-built" layouts and separation distances
Commissioning and service/desludging records
Pre/post CCTV and photos (especially for insurance or future sale)

FAQs

Can I convert a septic tank to a treatment plant to meet rules?

Often possible where space, power, and a compliant discharge route exist. Expect design, approvals, and commissioning records.

Do I always need a percolation test?

If you plan a drainage field, yes—test data underpins sizing and sign-off. For direct discharges from treatment plants, other evidence applies.

Are historic discharges automatically acceptable?

No. Replacement or upgrade work is assessed against current requirements, not past practices.

Can I mix surface water into foul drains?

Generally no. Keep systems separate unless a specific approved design states otherwise.

Related: Soakaway Regulations · Interceptor Traps