Buying a home with a septic tank, treatment plant or cesspool

What you take on

Whoever owns the property using a septic tank or treatment plant is its operator and responsible for it. If the system is shared with other properties, the owners are jointly responsible. A tenant can be the operator if the tenancy agreement says so.⁵

The operator must meet the Environment Agency's general binding rules, or hold a permit. A home connected to the public foul sewer needs neither.⁵Cesspools follow different rules (see below).⁶

Septic tank

An underground tank where solids sink to form sludge and the liquid flows out to a drainage field.²

Small sewage treatment plant

Also called a package plant. Works like a septic tank but uses mechanical parts to treat the water to a higher standard.²

Cesspool

Holds the sewage until it's emptied. If a system releases sewage into the ground or surface water, it isn't a cesspool.⁶

Already know the answers? Check them against the rules in a few questions.

Questions about the drainage

Ask the seller, through the estate agent or your solicitor. Under each: why the answer matters.

1. What is the system, and where does the liquid go?

   A septic tank must not discharge straight into a watercourse. If it does, the operator must connect to a sewer, fit a treatment plant or install a drainage field as soon as possible, with plans in place usually within 12 months. Gov.uk says buyer and seller should agree who pays for this as a condition of sale.¹

2. Can I have the seller's written details of the system?

   A seller must tell the new operator in writing that a sewage discharge is in place, with a description of the system, where its main parts and discharge point are, any changes made, how to maintain it (with the manual if they have it) and maintenance records if they have them.²¹

3. When was it installed, and has it been moved, switched or enlarged since?

   Discharges that started, moved more than 10 metres, switched between the ground and a watercourse, or went over the daily limit on or after 1 January 2015 have extra rules, and those from 2 October 2023 more again. Gov.uk tells buyers to check when the system was installed to work out whether it counts as new or existing.³²

4. Does it drain to a drainage field, a soakaway, or a well or borehole?

   A soakaway built for rainwater and installed after December 2007, or any well or borehole, can't meet the rules. The operator would have to upgrade to a drainage field, connect to a sewer, or apply for a permit.²

5. Did it meet the British Standard when it was installed?

   It must meet the standard in place at installation. Evidence is a CE mark, a certificate of compliance in its paperwork, or the product on British Water's approved list; the installer can also confirm. Systems from before 1983 are exempt from this one rule.²

6. Did it get building regulations approval, and planning permission if needed?

   If a system didn't get building regulations approval when it was installed, you may need to apply for it, and you might also need planning permission. For systems installed before 1 January 2015, gov.uk says to ask the local council about planning.⁴

7. When was it last emptied, and by which firm?

   Sludge must be removed before the tank is full; gov.uk says at least once a year or as the manufacturer says. Left too long, solids can be carried into the drainage field, causing damage and pollution. The firm must be a registered waste carrier.²

8. Is the system shared with other homes, or does anything else drain into it?

   If your property shares a system, you are jointly responsible for it. The limits are 2 cubic metres a day to the ground and 5 to surface water; if more is connected, the operator has to recalculate the daily volume and check the system is still big enough.⁵²

9. Is there a public sewer nearby?

   For discharges that started on or after 1 January 2015, a public foul sewer within 30 metres of any boundary of a single house means the rules can't be met. If you connect to a public foul sewer, the rules no longer apply and no permit is needed. Gov.uk says to ask the local water company, or neighbours.²⁵

10. Is the discharge near a drinking water source or a protected site?

    A ground discharge in groundwater source protection zone 1 (which includes any area within 50 metres of a private drinking water supply) needs a permit. Later discharges also can't be in or near certain protected sites. Magic map shows the zones and sites.²

Useful links from the rules: Magic map,find your water company andBritish Water's accredited service engineers(gov.uk notes there may be other competent engineers).²

Signs it isn't working, and smells

The rules say a septic tank or treatment plant must be repaired or replaced if it isn't in good working order, for example if it has:²¹

• leaks, or cracks in the tank walls or pipes
• blocked pipes
• pools of water around the drainage point
• sewage smells
• a failed motor, pump or electrical supply

So a sewage smell at a viewing is worth asking about: the rules name it as a sign that a system must be repaired or replaced. Anyone who maintains the system must be competent.²Gov.uk doesn't list causes of smells, so neither do we.

If you see sewage in a river, stream or other watercourse, report it to the Environment Agency online or on its 24-hour incident hotline, 0800 80 70 60.⁷A smell coming from a neighbour's property is for the local council's environmental health team.⁸

If it's a cesspool

• The general binding rules don't apply.⁶
• It must be kept maintained, emptied regularly by a registered waste carrier (gov.uk's example is once a month), and must not leak or overflow.⁶
• No permit is needed unless the Environment Agency says so.⁶
• The Environment Agency or the council can make the owner repair or replace a cesspool in poor condition, and a cesspool that causes pollution breaks the law.⁶
• A new cesspool needs planning permission and building regulations approval, and must hold at least 18,000 litres for 2 users plus 6,800 litres for each extra user.⁶

So ask how often it's emptied, by whom, and whether it has ever leaked or overflowed. We haven't found an official source for typical emptying costs, so we don't quote any.

If the water is a private supply

A private water supply is any drinking water supply not provided by a water company. Sources include boreholes, springs and watercourses. About 1% of people in England use one. Councils regulate them; the Drinking Water Inspectorate advises councils.⁹

Once you buy, you become a "relevant person" for the supply, and the council can serve you a notice to put problems right. The Inspectorate advises buyers to check the deeds for agreements about who maintains the supply, and to get legal advice.¹⁰

Questions the Drinking Water Inspectorate suggests

1. Are there deeds or agreements, formal or informal, saying who maintains and runs the supply or parts of it?
2. Has the council risk assessed the supply? When, and what did it find? Did it ask for improvement works, and were they done?
3. What did any council sampling show? Was there ever a quality problem or a risk to health?
4. Is there treatment, such as filters or a UV unit? Was it fitted by a competent installer, and is a UV unit sized for drinking water?
5. Are there maintenance logs or records?
6. Have there been problems with taste, smell, colour or the supply running short?
7. Are there written instructions for what to do if the supply fails, with contacts for alternative water and repairs?
8. Is there a plan of the pipes, tanks, chambers and treatment?

Shortened from the Inspectorate's list.¹⁰

Testing

A supply to more than one home must be risk assessed every five years and tested regularly by the council. A supply to a single home that isn't let or used for a business doesn't have to be tested unless the owner or occupier asks, or the council thinks there's a risk to health.¹⁰Without results, the water quality may be unknown, so the Inspectorate recommends buyers ask the council for a risk assessment and testing. There's a fee.¹⁰One test isn't the whole picture: quality can change with the seasons.¹¹

Your council

In Bath and North East Somerset, North Somerset or Swindon, ask that council's environmental health team: councils are the regulators.⁹

Who to contact

Whether a discharge meets the rules, or needs a permit

Environment Agency, 03708 506 506 (Monday to Friday, 8am to 6pm) orenquiries@environment-agency.gov.uk.¹⁵

Sewage in a river, stream or other watercourse

Environment Agency incident hotline, 0800 80 70 60, 24 hours.⁷

Where the nearest public sewer is

The local water company. Find yours.²

Whether an emptying firm is a registered waste carrier

Ask the firm, or the tanker driver for the certificate, or search theEnvironment Agency's register.²¹⁴

A private water supply

The council's environmental health team.⁹

The 155 firms we've checked so far, including 49 that say they empty tanks. It's a short list, not a complete one.

Guides: A smell from the septic tank: what the rules say, Cesspools and cesspits: the rules in England, Septic tank general binding rules in plain English