You must read septic tanks and treatment plants: permits and general binding rules before you follow this guidance.
New rules came into force on 1 January 2015. If your system was installed and discharging before 31 December 2014 you have an ‘existing discharge’. If your system was installed and discharging on or after 1 January 2015 you have a ‘new discharge’.
Rules for existing and new discharges
Use the correct treatment system
You must use a septic tank or small sewage treatment plant to treat the sewage and then discharge the effluent (treated liquid) to ground via a drainage field.
A septic tank is an underground tank where the solids sink to the bottom, forming a sludge, and the liquid flows out to a drainage field.
A small sewage treatment plant, also known as a package treatment plant, works in a similar way to a septic tank but uses mechanical parts to treat the liquid to a higher standard before it goes to a drainage field.
A drainage field, also known as an infiltration system, is a series of pipes with holes placed in trenches and arranged so that the effluent can trickle through the ground for further treatment.
You cannot use a soakaway (designed for draining rainwater), well or borehole for discharging effluent to ground. Instead you must either upgrade to a drainage field or apply for a permit so that the Environment Agency can assess the risk of using this sort of system in your location.
Your treatment system must meet the right British Standard
Your treatment system must meet the relevant British Standard in force at the time of installation. The standards currently in force for new systems are:
- BS EN 12566 for septic tanks and small sewage treatment plants
- BS 6297:2007 for drainage fields
Your septic tank or treatment plant met the British Standard in place at the time of installation if:
- it has a CE mark
- the manual or other documentation that came with your tank or treatment plant has a certificate of compliance with a British Standard
- it’s on British Water’s list of approved equipment
You can also ask the company that installed your equipment to confirm that it complies with the British Standard that was in place at the time the equipment was installed.
If your treatment system was installed before 1983 there was no British Standard in place. You do not need to do anything to meet the British Standard requirement. You must still meet all the other general binding rules.
Your treatment system must be installed correctly and have enough capacity
Your treatment system must be large enough to handle the maximum amount of sewage it will need to treat. If you install a new septic tank, small sewage treatment plant or drainage field you must check with the installer that it meets the sizing requirements in British Water’s Flows and Loads 4 guidance.
If the amount of sewage the system needs to treat increases (for example, because you’ve extended your property or connected an additional property) you must make sure the treatment system is still big enough. You must also recalculate the maximum daily volume of your discharge and apply for a permit if it is more than 2 cubic metres (2,000 litres) a day.
Your treatment system must be installed in line with the manufacturer’s specification (the instruction manual or technical set of requirements that comes with the equipment).
Have your treatment system regularly emptied and maintained
You must get the sludge that builds up in your septic tank or small sewage treatment plant removed (desludged) before it exceeds the maximum capacity. As a minimum, you should have your treatment system desludged once a year or in line with the manufacturer’s instructions.
The company you use to dispose of your waste sludge must be a registered waste carrier. Ask the company to confirm this when you arrange to have your tank emptied or ask the tanker driver for a copy of the company’s waste carrier certificate.
You should have your treatment system regularly maintained in line with the manufacturer’s instructions. If these are not available, ask your local maintenance company for advice.
You must have your treatment system repaired or replaced if it is not in good working order, for example if it has:
- cracks in tank walls or pipes
- blocked pipes
- signs that the effluent is not draining properly, pools of water around the drainage point
- sewage smells
- a failed motor
- a failed pump
- a failed electrical supply
Anyone who carries out maintenance on your system must be competent. Competent people include those on British Water’s list of accredited service engineers.
You sell your property: tell the new owner about the sewage treatment system
If you sell your property, you must tell the new operator (the owner or person responsible for the septic tank or small sewage treatment plant) in writing that a small sewage discharge is in place.
- a description of the treatment system and drainage system
- the location of the main parts of the treatment system, drainage system and discharge point
- details of any changes made to the treatment system and drainage system
- details of how the treatment system and drainage system should be maintained, and the maintenance manual if you have one
- maintenance records if you have them
You stop using your treatment system: make sure it’s properly decommissioned
You must remove anything that could cause pollution (for example, remaining sludge) when you stop using a septic tank or small sewage treatment plant.
This does not apply if you only stop using the equipment temporarily, for example if your property is empty.
You can ask a maintenance company for advice on how to decommission your septic tank or treatment plant properly.
Rules for discharges in a groundwater source protection zone 1 (SPZ1)
Check if the discharge point is in a groundwater SPZ1
A groundwater SPZ1 can be either:
- the area around a commercial water supply (used for drinking water or food production) shown on the map of protected zones – check if your discharge is in the inner zone (zone 1) or ask the Environment Agency
- any area within 50 metres of a private water supply for human consumption – ask your neighbours if they have one and if so how far their spring, well or borehole is from your drainage field
You must apply for a permit if you have an existing discharge or are planning to start a new discharge to the ground in a SPZ1. The permit costs £125. A permit will include additional conditions to the general binding rules.
The Environment Agency will grant the permit if there’s:
- no evidence of pollution
- the risk of pollution is acceptable
If there is evidence of pollution or the risk of pollution is unacceptable the Environment Agency will ask you to make changes to your system and may issue a permit with improvement conditions.
The Environment Agency regularly checks:
- surface and groundwater quality
- permit compliance
If they find your system may be causing pollution to surface or groundwater they will contact you to discuss the issues. This may result in your permit being reviewed or revoked. See the guidance on how to comply with your permit.
Additional rules for new discharges from treatment systems installed and in use on or after 1 January 2015
You must follow these additional rules if you:
- started a new discharge from a septic tank or small sewage treatment plant on or after 1 January 2015
- had a discharge to a surface water before 1 January 2015 which you now want to change to discharge to ground, or the other way round
- had a discharge to ground before 1 January 2015 and you want to install a new drainage field more than 10 metres away from the existing one
These are called new discharges.
Check if there’s a public sewer nearby
If any part of the building your treatment system serves is within 30 metres of a public sewer, the Environment Agency will not allow you to start a new discharge from a septic tank or small sewage treatment plant under the general binding rules.
If you are building a development of more than one property, this distance must be multiplied by the number of properties – for example, if there are 3 properties then the distance will be 3 x 30 metres = 90 metres.
To find out if there is a public sewer near your property, contact your local water company.
If there is a good reason why you cannot connect to the sewer (for example, if there is a river or a hill in the way) then you must apply for a permit so that the Environment Agency can decide whether to allow you to use a small sewage treatment plant instead. Contact the Environment Agency to find out what information you will need to put in your application.