Septic Tank Compliance Certificate

If your property is not connected to the public sewer and relies on a septic tank, cesspit, or sewage treatment plant to manage foul water, drainage compliance will be a significant focus of your conveyancing. Since the Environment Agency introduced revised General Binding Rules in January 2020, the rules around what private drainage systems can legally do have tightened considerably, and many older septic tanks across England no longer meet the required standard.

Unlike a gas safety certificate or an electrical installation condition report, there is no single official document called a “septic tank compliance certificate.” What buyers and their solicitors are looking for is evidence that your system is operating lawfully under current Environment Agency regulations. This guide explains what those regulations require, what documentation you need to provide, and how to handle the sale if your system has not yet been upgraded.

Understanding the General Binding Rules

The General Binding Rules (GBRs) for small sewage discharges came into force in England on 1 January 2020, replacing the previous exemption registration system under the Environmental Permitting (England and Wales) Regulations 2016. They represent a significant tightening of the rules around private drainage systems.

The key change introduced by the GBRs is straightforward but consequential: septic tanks may no longer discharge directly to surface water. Surface water means any ditch, stream, river, drain, or other watercourse, even if it appears dry for much of the year. If your septic tank currently discharges into such a watercourse, it is in breach of the GBRs unless you hold a bespoke Environment Agency permit specifically authorising that discharge.

Under the GBRs, a compliant septic tank must discharge only to the ground through a properly designed and installed drainage field (soakaway). If a drainage field is not feasible — for example, because the soil is too clay-heavy or the water table is too high — the septic tank must be replaced with a sewage treatment plant that produces a cleaner effluent standard suitable for surface water discharge.

Who is affected?

The GBRs apply to all properties in England with private sewage systems that discharge to surface water. This includes:

• Older rural properties, farmhouses, and cottages where the historical drainage arrangement was to a nearby ditch or stream
• Properties where extensions or increased occupancy have overloaded an older system not designed for the current demand
• Any property where the drainage field has failed and the overflow is reaching a watercourse

If you are unsure whether your system discharges to surface water or to the ground, a drainage surveyor can carry out a site assessment and a percolation test to establish how the system works and whether it complies.

What sellers must disclose on the TA6 form

The TA6 Property Information Form is the primary disclosure document in an English or Welsh residential sale. It asks sellers to provide detailed information about the property's drainage arrangements, and the answers you give here will directly shape the enquiries raised by the buyer's solicitor.

In the drainage section, sellers with private systems must confirm:

• Whether the property drains to the public sewer, a cesspit, a septic tank, or a sewage treatment plant
• The type and approximate age of the system
• Whether the system has any Environment Agency registration, exemption, or permit in place
• Whether the system has been maintained regularly, including records of desludging (emptying)
• Whether there are any known defects, failures, or compliance issues with the current system

Providing inaccurate or incomplete information on the TA6 is a serious legal risk. If a buyer suffers loss as a result of a drainage non-compliance you knew about but did not disclose, they may have grounds for a misrepresentation claim against you after completion. The safest approach is to gather all available documentation about your system and be fully transparent.

For an overview of the full range of paperwork involved in a sale, see our guide on what is in a property certificate pack.

Types of compliant drainage systems

Understanding the difference between the main types of private drainage system helps you explain your system accurately to buyers and their solicitors.

Environment Agency permits and registrations

Before the GBRs came into force, it was possible to register a “small sewage discharge to surface water” exemption with the Environment Agency under the Environmental Permitting Regulations. These exemptions allowed septic tanks to discharge to surface water legally, provided the system met certain conditions relating to tank size, distance from watercourses, and quality of discharge.

Since 1 January 2020, new exemption registrations for septic tank surface water discharges are no longer possible. Existing registered exemptions may still be in place for some systems, but there is a critical issue for sellers: exemption registrations under the old scheme are held by the individual who registered them and cannot be transferred to a new owner. This means that even if your system has a registered exemption, a buyer taking ownership of the property cannot simply inherit it — they would need to apply for a bespoke Environment Agency permit or upgrade the system.

If your system holds a bespoke permit (rather than a standard exemption), you should provide this documentation to your solicitor. Bespoke permits may include conditions relating to the quality of discharge, maintenance requirements, and monitoring obligations, all of which the buyer will need to be aware of.

What happens if your system is non-compliant?

Discovering that your septic tank is non-compliant does not necessarily prevent you from selling, but it does require a decision about how to proceed. There are broadly three approaches:

Option 1: Upgrade before you sell

Upgrading the system — either by installing a drainage field or replacing the septic tank with a sewage treatment plant — before listing your property removes the compliance issue entirely. The property can then be marketed as having a compliant drainage system, which avoids any buyer concern or price negotiation on this point. This approach is particularly advisable if you expect to attract buyers who are relying on a mortgage, as lenders may be reluctant to lend on properties with known environmental non-compliances.

Typical upgrade costs are:

• New drainage field installation: £2,000 to £6,000 depending on ground conditions, size, and access
• Sewage treatment plant supply and installation: £4,000 to £10,000 for most residential properties
• Percolation test (to confirm ground suitability for a drainage field): £300 to £600

Option 2: Disclose and adjust the price

If you prefer not to carry out the upgrade before selling, you can disclose the non-compliance fully on the TA6 form and allow buyers to factor the cost of remediation into their offer. This is a legitimate approach, but be prepared for buyers to seek a reduction that reflects not only the direct cost of the upgrade but also the inconvenience and uncertainty involved. Some buyers, particularly those using mortgage finance, may withdraw if their lender refuses to lend on the property in its current state.

This situation shares similarities with other building compliance issues. For further context, see our guides on missing building regulations sign-off and selling a house with drainage problems.

Option 3: Indemnity insurance

In some limited cases, buyers and their solicitors may accept an indemnity insurance policy to cover the risk of enforcement action by the Environment Agency. However, indemnity insurance for active environmental breaches is not always available, and insurers will typically only provide cover if the breach has been in existence for some time and there is no known enforcement action already under way. You should not assume this option is available without specific advice from your solicitor and a specialist insurance broker.

The drainage survey: what buyers will want

Buyers purchasing properties with private drainage systems — particularly in rural areas — increasingly commission a specialist drainage survey as part of their due diligence. A drainage survey for a septic tank system typically includes:

• A CCTV camera inspection of the drainage pipework and the internal condition of the tank
• An assessment of the drainage field or soakaway, including signs of saturation, failure, or surface breakout
• Identification of the discharge point and whether it complies with the General Binding Rules
• A check of the Environment Agency's public register for any registrations or permits associated with the property
• A written report with recommendations for any remedial work

If a drainage survey identifies problems after a buyer has made an offer, you will typically face a renegotiation. Commissioning your own drainage survey before listing gives you the opportunity to address any issues — or at least to understand the cost of doing so — before a buyer is involved. It also signals to buyers that you have been thorough in your sale preparation, which builds confidence.

Documentation to gather as a seller

When selling a property with a private drainage system, gathering the following documents before instructing your solicitor will help to answer TA6 questions fully and reduce the likelihood of protracted enquiries:

• Any Environment Agency exemption registration or bespoke permit documentation
• Planning permission and building regulations approval for the original installation or any subsequent upgrades
• The drainage field design and installation records (if available)
• Records of regular desludging by a licensed waste carrier, including dates and frequency
• Any maintenance records for a sewage treatment plant, including servicing by the manufacturer or approved engineer
• Results of any percolation test carried out on the land
• Any correspondence with the Environment Agency or local authority about the drainage system

Even if some of these documents are missing — which is common for older systems — providing what you do have demonstrates good faith and helps buyers assess the situation. For context on the broader costs that can arise when documentation is incomplete, see our guide on the hidden costs of selling a house.

How septic tank compliance interacts with the property searches

It is worth understanding that the standard property searches carried out during a conveyancing transaction do not specifically assess whether a private drainage system complies with the General Binding Rules. The drainage and water search (CON29DW) confirms whether the property is connected to the public sewer network, but it says nothing about the legality or condition of a private system.

Compliance with the Environment Agency's GBRs is an environmental regulation matter, not a local authority search matter. This is why it falls to sellers to disclose it via the TA6 form and why buyers are well advised to commission a specialist drainage survey in addition to the standard searches.

For properties where there is any uncertainty about the discharge point, the Environment Agency maintains a public register of water discharge activity permits and exemptions, which solicitors and drainage surveyors can check as part of their due diligence.

Seller's checklist for septic tank compliance

1. Identify how your system currently discharges — to a drainage field in the ground, or to a surface watercourse
2. If you discharge to surface water, check whether you hold a bespoke Environment Agency permit and obtain a copy
3. If your system is non-compliant, get quotes for upgrading to a drainage field or a sewage treatment plant before deciding whether to upgrade or disclose
4. Arrange a drainage survey to establish the current condition and compliance of the system
5. Gather maintenance records, desludging receipts, planning documents, and any permit or exemption paperwork
6. Complete the drainage section of the TA6 form accurately and attach all supporting documentation
7. Disclose any known defects or failures honestly — concealing drainage problems creates significant legal risk after completion
8. Be prepared for buyers to commission their own drainage survey and factor potential issues into their offer

Sources

• Environment Agency — General binding rules for small sewage discharges (GOV.UK)
• Environmental Permitting (England and Wales) Regulations 2016 — legislation.gov.uk
• Environment Agency — Septic tanks and sewage treatment plants: what you must do (GOV.UK, updated January 2020)
• Law Society — Property Information Form (TA6), 4th edition
• Environment Agency — Public register of water discharge activity permits and exemptions
• Building Regulations 2010, Part H — Drainage and waste disposal (GOV.UK)

Related guides

• Selling a Cottage in the UK

Frequently asked questions