Septic tank general binding rules in plain English

What the rules are

The general binding rules cover septic tanks and small sewage treatment plants that discharge waste water in England. Northern Ireland, Scotland and Wales have separate guidance ¹. If you meet all the rules that apply to you, you do not need an environmental permit ¹.

If your system connects to the mains sewer, you do not need a permit ³. Cesspools follow different rules ³.

Which rules apply depends on whether your discharge is existing or new. A discharge is new if it started or changed significantly since 2 October 2023 ³.

Discharge to ground

A septic tank can discharge to ground through a drainage field ¹. You must not discharge effluent from a septic tank to a watercourse ¹.

Key points:

• The limit is 2 cubic metres (2,000 litres) a day to ground ¹.
• Above that, you must connect to the public foul sewer where reasonable. If that is not reasonable, you must apply for a permit ¹.
• The sewage must be domestic in nature and must not cause pollution ¹.
• Using a well or borehole means you cannot meet the rules, and neither can a soakaway installed after December 2007 ¹.
• Systems installed before 1983 do not need to meet a British Standard, but must meet the other rules ¹.

Discharge to surface water

For discharge to a surface water, the limit is 5 cubic metres (5,000 litres) a day ². Above that, you must connect to the public foul sewer where reasonable, or apply for a permit ².

A septic tank that discharges directly to a watercourse must change ². As soon as possible, you must do one of the following ²:

• connect to a public foul sewer
• replace the septic tank with a small sewage treatment plant
• install a drainage field and meet the rules for discharge to ground

You must have plans in place to do this within a reasonable timescale, usually 12 months ².

The 1 January 2020 date appears only in the page’s change history. A July 2018 entry said that where a property with such a septic tank was sold before 1 January 2020, the buyer and seller should address who replaces or upgrades the system ². A later entry, from 25 October 2019, says you need to act as soon as possible ². The current page sets no fixed deadline date ².

You must have building regulations approval if you have or are planning to install a new septic tank or sewage treatment plant. You may also need planning permission ¹².

Selling or buying a property

If you sell, you must tell the new operator in writing that a sewage discharge is in place ¹². Include ¹:

• a description of the treatment and drainage systems
• the location of the main parts and the discharge point
• any changes you have made
• maintenance details and the manual, if available
• maintenance records, if available

If the septic tank discharges directly to a watercourse, agree with the other party who will replace or upgrade the system. Agree this as a condition of sale ².

Emptying and maintenance

• Empty sludge before the tank reaches its maximum capacity. Do this at least once a year, or as the manufacturer’s instructions say ¹².
• Use a registered waste carrier. Ask the company to confirm this, or ask for the carrier’s certificate ¹².
• Maintain the system as the manufacturer’s instructions say. If you have none, ask a local maintenance company ¹.
• Maintenance should be done by competent people, such as British Water’s accredited service engineers ¹.
• Repair or replace the system if it is not in good working order. Signs include leaks, cracks in tank walls or pipes, blocked pipes, pools of water around the drainage point, sewage smells, or a failed motor, pump or electrical supply ¹.

If you extend the property or connect another property, work out the maximum daily volume again. Check the system is still large enough ¹.

When you need a permit

You need a permit if you cannot meet all the rules that apply, and you cannot connect to a public sewer or change your system to meet them ¹².

Examples for ground discharges include ¹:

• a discharge point in groundwater source protection zone 1 (SPZ1, except SPZ1c). A groundwater SPZ1 can also be any area within 50 metres of a private water supply for human consumption
• a discharge in ancient woodland
• a discharge within 50 metres of certain protected sites, such as a special area of conservation or a biological SSSI

Examples for surface water discharges include ²:

• a discharge to a ditch or watercourse that does not flow all year
• a discharge to an enclosed lake or pond
• a discharge within 500 metres of certain protected sites

New discharges from 2 October 2023 also need a permit if they share an outlet and the combined volume is over the limit. The same applies if they are within 50 metres of another system using the general binding rules ¹².

Where to get help

If you cannot meet the rules, contact your sewerage undertaker about connecting to a public foul sewer ¹. The rules are set out in full on the GOV.UK pages listed as sources for this guide ¹²³.