Septic tank soakaway regulations 2020: what the 2020 rule banned (a septic tank discharging to a watercourse), what happened to the deadline (withdrawn 25 October 2019, now 'as soon as possible'), what it never touched (a drainage field to ground), the drainage mound, and the rules a soakaway must meet in England and Scotland
- The 2020 rule is about where the effluent goes, not about soakaways. The 2015 guidance said a septic tank discharging directly to surface water had to be replaced or upgraded by 1 January 2020, or on sale if earlier; the date was withdrawn on 25 October 2019 and the current gov.uk text says as soon as possible, with plans in place within usually 12 months. Discharges from septic tanks to watercourses are not allowed under the rules. A septic tank to a drainage field in the ground was, and is, allowed.
- Discharge to ground has its own rules: 2 cubic metres a day or less (rule 1), treatment by a septic tank and infiltration system, which gov.uk defines as a drainage field, a series of pipes with holes placed in trenches (rule 5), not within source protection zone 1 or 50 metres of a well, spring or borehole (rule 7). Outside the rules you need a permit, quoted at £117 for discharge to ground.
- What the word means in the rules: the general binding rules exclude a rainwater soakaway installed after December 2007; the drainage field is not that pit. Approved Document H sites it 10 m from a watercourse, 50 m from a water abstraction, 15 m from a building, downslope of water sources, with no drives or services over it, and allows it only where the percolation value Vp is between 12 and 100.
- The drainage mound is the same thing built above ground: Approved Document H treats fields and mounds together (§1.26–1.44), SEPA says a soakaway includes mound soakaways for slow percolation or shallow bedrock, and a Scottish self-builder describes one fed by a holding tank and pump 25 metres away. Separation from groundwater: more than 1 metre in winter (SEPA), 1.2 m under BS 6297 as reported.
- Size: At = p × Vp × 0.25; four people on ground with Vp 40 need 40 m², about 67 m of 600 mm trench, in loops of perforated pipe on 300 mm of 20–50 mm stone, 500 mm below the surface, 2 m of undisturbed ground between trenches, an inspection chamber before the field, gradient no steeper than 1:200.
Discharge to ground under the general binding rules carries four conditions a household has to meet. Rule 1: 2 cubic metres a day or less, a limit a house is far inside. Rule 4: no pollution of surface water or groundwater. Rule 5: treatment by a septic tank and infiltration system, or by a sewage treatment plant and infiltration system. Rule 7: not within groundwater source protection zone 1 or within 50 metres of any well, spring or borehole used to supply water for domestic or food production purposes. Discharges started on or after 2 October 2023 pick up extra siting rules, and anything outside the rules needs an environmental permit, with fees quoted at £117 for discharge to ground and £292 for discharge to a watercourse. Approved Document H then supplies the distances for building control: at least 10 m from any watercourse or permeable drain, at least 50 m from the abstraction point of a groundwater supply, at least 15 m from any building, and far enough from other fields, mounds or soakaways that the soakage capacity of the ground is not exceeded.
The document adds the conditions that owners forget: the disposal area downslope of groundwater sources, no water supply pipes or other services in it, and no access roads, driveways or paved areas over it. A Screwfix member compresses it into one line, 15 m from the property and 10 m from any watercourse, and adds the part that building inspectors stress: it is not the area that matters but the length of pipe, calculated from the porosity of the ground and the number of people. That calculation is §1.44, At = p × Vp × 0.25, valid only where the percolation value lies between 12 and 100.
The permit route is worth knowing because it is cheaper than people fear and because it is sometimes unavoidable: a field that cannot keep 50 m from a neighbour's borehole, or a site inside source protection zone 1, cannot use the binding rules at all, and the Environment Agency will either permit the discharge with conditions or refuse it. The quoted fee of £117 for a discharge to ground is small against the cost of the field; what costs is the groundwater risk assessment the agency may ask for, and the time. A consultant working on high water table sites notes that where separation distances or soil conditions cannot be achieved an environmental permit may be required, which is the polite way of saying the field is not a right.
Distances are measured from the field, not from the tank, and from the point of abstraction, not the boundary of the neighbour's land, so a borehole 40 m away that the owner never mentioned is a defect in your system rather than theirs. Before any digger arrives, ask the neighbours on every side whether they draw water, and look for the chalk and sand that Part H lists as good ground; on sandy clay, silty clay or clay the document says percolation is poor, and the test will say the same more expensively.
Search “septic tank regulations 2020 soakaway” and you will find two camps: pages saying soakaways were banned in 2020, and pages saying nothing changed. Neither is right. The 2020 rule banned one thing, a septic tank emptying into a stream; it left the drainage field in the ground exactly where it was, with its own set of rules that most owners have never read. This guide puts the rule, the field and the mound side by side.
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What the 2020 rule banned, and what it did not
The general binding rules for small sewage discharges in England set a deadline for one configuration only. The guidance published in 2015 said: if you have a septic tank that discharges directly to a surface water you will need to replace or upgrade your treatment system by 1 January 2020, or when you sell your property if before this date. The reason was in the same guidance: discharges from septic tanks directly to watercourses are not allowed under the general binding rules, because a septic tank only settles sewage and a stream cannot finish the job. The date itself did not survive to 2020. It was removed in updated guidance published on 25 October 2019, as the law firm Gateley recorded two weeks later, and the current text on gov.uk reads: if your septic tank discharges directly to a watercourse, as soon as possible you must connect to a public foul sewer, replace your septic tank with a small sewage treatment plant, or install a drainage field, and you must have plans in place to do this work within a reasonable timescale, usually 12 months. The prohibition stayed; the cliff edge went. The two lawful options were, and are, a treatment plant discharging to the watercourse, which rule 6 requires for any discharge to surface water, or a septic tank discharging to ground through a drainage field.
Nothing in that rule mentions soakaways, and nothing in it bans discharging to ground. Rule 5 for discharges to ground says the sewage must receive treatment from a septic tank and infiltration system, which the guidance defines as a drainage field, or from a sewage treatment plant and infiltration system. So a septic tank with a drainage field was the compliant arrangement before 2020 and is the compliant arrangement after it. What the rules do exclude is the other thing the word covers: a soakaway designed for draining rainwater installed after December 2007 is outside the rules altogether, because a rainwater pit is not a treatment system. The full list of the rules, sorted by the date your discharge started, is in the general binding rules explained.
The rules a drainage field has to meet
Discharge to ground has four binding rules that matter to a household. Rule 1: 2 cubic metres or less a day, which gov.uk elsewhere states as the limit for an infiltration system or drainage field; a normal house is well inside it. Rule 4: the discharge must not cause pollution of surface water or groundwater. Rule 5: treatment by a septic tank and infiltration system, or a treatment plant and infiltration system. Rule 7: not within groundwater source protection zone 1 or within 50 metres from any well, spring or borehole used to supply water for domestic or food production purposes. New discharges started on or after 2 October 2023 carry further siting conditions, and a discharge that cannot meet the rules needs an environmental permit from the Environment Agency, with application fees quoted at £117 for discharge to ground and £292 for discharge to a watercourse.
Building control then applies Approved Document H, which is where the distances come from. §1.27: a drainage field or mound should be located at least 10 m from any watercourse or permeable drain, at least 50 m from the point of abstraction of any groundwater supply and not in any zone 1 groundwater protection zone, at least 15 m from any building, and sufficiently far from any other drainage fields, drainage mounds or soakaways so that the overall soakage capacity of the ground is not exceeded. §1.28 puts the disposal area downslope of groundwater sources; §1.29 and §1.30 keep water pipes, services, access roads, driveways and paved areas out of it. A Screwfix member summarises it the way building inspectors say it.
The drainage (leach) field needs to be 15m from the property, it also has to be 10m from any watercourse and away from other drainage fields. It's not so much a question of area but rather the length of drainage pipe in the field that matters. You have to calculate that based on the porosity of the soil (via a percolation test) and the throughput.
community.screwfix.com, thread "Sceptic tank"The calculation he refers to is §1.44: At = p × Vp × 0.25, the floor area in square metres from the number of persons and the percolation value in seconds per millimetre, measured in a 300 mm square hole as §1.34 describes, and valid only where Vp lies between 12 and 100 (§1.38). Four people on ground with Vp 40 need 40 m²; divided by a 600 mm trench that is about 67 m of pipe. Below 12 the effluent reaches groundwater too fast, above 100 it does not soak away, and in either case §1.38 says a drainage field should not be used, although a treatment plant with a soakaway may still be possible. The test method, the colour test for soil and the formula step by step are in the drainage field explained.
| Requirement | Source |
|---|---|
| ≤ 2 m³/day | Rule 1 |
| No pollution of surface or groundwater | Rule 4 |
| Septic tank + infiltration system | Rule 5 |
| Not in SPZ1; ≥ 50 m from well, spring, borehole | Rule 7 |
| ≥ 10 m watercourse; ≥ 15 m building; downslope of water sources | ADH §1.27–1.28 |
Permit outside the rules: £117 to ground, £292 to a watercourse (quoted fees).
The drainage mound: the same field, built above the ground
Approved Document H never treats the mound as a separate device: §1.26 gives guidance on design and construction of drainage fields and drainage mounds together, and §1.39 requires both to ensure aerobic contact between the liquid effluent and the subsoil. A mound is the answer when trenches cannot be dug to the required depth above the water table, when percolation is slow, or when rock is close to the surface; the field is raised in imported granular material and, because the effluent now has to go uphill, it is fed by a pump from a chamber after the tank. SEPA says it in one line: a soakaway also includes mound soakaways, a type of soakaway built above ground where percolation is slow or where digging trenches may be too difficult, for example where bedrock is close to the surface. A Scottish self-builder on Screwfix describes the real thing.
If the percolation tests are unsatisfactory, you can get round it by building an above ground mounded soakaway with a pumped system.
community.screwfix.com, thread "Septic tank & scottish building regulations"In our case the percolation in our own plot was too poor, but we had permission to install the soakaway under an adjoining field. This land was higher so a holding tank and pump were needed. Odly there were no regs on the siting of this holding tank, so this is located less than 10 metres from a watercourse.
community.screwfix.com, thread "Septic tank & scottish building regulations"His pump chamber held a single submersible stainless steel pump with a float switch, and 25 metres of 50 mm pipe ran up to the soakaway five metres higher; the sample chamber between tank and pump is a SEPA requirement. The groundwater separation that justifies a mound is stated differently north and south of the border: SEPA wants the highest seasonal water table, in winter, more than one metre below the base of the soakaway; a consultant working in England cites BS 6297 as requiring no part of the infiltration system to be less than 1.2 metres above the highest predicted annual groundwater level, and adds that the level must be measured in the wetter months because summer readings can be misleading, with the trial hole excavated to at least 1.2 m. Where the separation cannot be achieved, the same consultant notes, an environmental permit may be required. What the mound is built on, and what it costs, is in soakaway crates and what they are for, which also explains why crates are a rainwater product.
How a field is built, to the millimetre
The construction rules are short and they are the ones that inspectors check. §1.40: perforated pipe laid in trenches of a uniform gradient not steeper than 1:200. §1.41: pipes on a 300 mm layer of clean shingle or broken stone graded between 20 mm and 50 mm. §1.42: trenches filled to 50 mm above the pipe and covered with geotextile to keep silt out, the rest filled with soil, distribution pipes at a minimum depth of 500 mm below the surface, trenches 300 to 900 mm wide, with areas of undisturbed ground 2 m wide between parallel trenches. §1.43: an inspection chamber between the septic tank and the field. §1.44: the field set out as a continuous loop fed from that chamber. A Screwfix member gives the site version of the same spec.
Typical soakaway is a trench either 600 or 900mm wide, 450mm depth of clean drainage stone in the bottom into which you lay rigid perforated effluent pipe (not the bendy stuff that comes on a coil).
community.screwfix.com, thread "soak away"The two details that fail most fields are in those paragraphs: coiled land drain instead of rigid perforated pipe, and trenches cut too close together so that the 2 m of undisturbed ground, the part that actually treats, is missing. A DIYnot member working out a 48 m² field asked where its edge lies in relation to the pipes, was told a metre outside them, and then found the better answer in BS 6297 section 6.3: only the area of the trenches themselves counts, not the land between, so 48 m² at a 500 mm trench width is 96 m of trench, which in four branches with the 2 m gaps occupies 24 m by 8 m, 144 m² of ground. He also noticed that section 6.7 of the standard asks for undisturbed ground greater than 1 m wide between trench sides where Part H says 2 m; building control works to Part H. The same thread records the failure that clay produces: the emptied tank refills through the outlet because the surrounding soil is waterlogged. What a working field needs from the tank side, baffles, a T-piece and a settled effluent, is in how a septic tank works.
Scotland: the same system, a different word and a register
In Scotland the vocabulary is reversed and the regulator is different. SEPA defines a soakaway as a sealed system of gravel filled trenches that allows the safe discharge of sewage effluent to the surrounding land, sometimes referred to as an infiltration system; the rainwater pit is not what it means. Construction follows the Building Standards Technical Handbook under local authority building control and needs a building warrant; the discharge itself is registered with SEPA. The siting rules: at least 10 metres from any permeable drain, watercourse, loch or the sea; no drinking water supply within 50 metres of the discharge for one to three houses, or within 250 metres for four to ten; the highest seasonal water table more than one metre below the base; and a soil percolation test by a specialist drainage contractor, with separate guidance when the value exceeds 100 s/mm. A Screwfix member summarises the building standard distances for a new tank, 5 metres from a building, 5 from a boundary or road, 10 from a watercourse, and the same for the soakaway. Registration, CAR licences and the phosphate catchments are in septic tank regulations in Scotland.
If your septic tank outlet runs to a ditch, stream, pond or land drain, the rule behind the 2020 date applies to you now, as soon as possible and with a plan within about 12 months, and the fix is a treatment plant or a drainage field, not a bigger pipe. If it runs to a drainage field, the 2020 rule does not apply, but rules 1, 4, 5 and 7 do: check the distance to any well or borehole, keep the field free of drives and services, and keep the emptying records. And do not let anyone sell you rainwater crates as a sewage soakaway: the binding rules exclude them, and Part H does not describe them.
The 2020 rule is the most misquoted sentence in British sanitation because it contains the word "replace", because the date was withdrawn two months before it fell and almost nobody went back to correct their page, and because sellers of treatment plants have had six years to let owners assume it applies to them. It applies to a septic tank that discharges to a watercourse, full stop. The drainage field in the ground is governed by older and duller text, Part H and rules 1 to 7, and that text is where the real obligations sit: distances, percolation, groundwater, construction. A homeowner who reads §1.27 and §1.44 knows more about whether their system is legal than one who has read every article about 2020, and if the ground is wet or rocky, the mound is not a loophole but the version of the same rules written for their soil.
2 cubic metres a day or less under rule 1.
At least 50 metres from any well, spring or borehole used for domestic or food supply, and not in source protection zone 1 (rule 7).
15 m from a building and 10 m from a watercourse or permeable drain (Approved Document H §1.27).
Frequently asked questions
Were septic tank soakaways banned in 2020?
No. The 2020 date in England's general binding rules concerned septic tanks that discharge directly to surface water, a ditch, stream or river: the 2015 guidance said that if you have a septic tank that discharges directly to a surface water you will need to replace or upgrade your treatment system by 1 January 2020, or when you sell your property if before this date. That date was removed from the guidance on 25 October 2019; the current text says that if your septic tank discharges directly to a watercourse, as soon as possible you must connect to a public foul sewer, replace the tank with a small sewage treatment plant or install a drainage field, with plans in place within a reasonable timescale, usually 12 months. Discharges from septic tanks directly to watercourses are not allowed under the rules. A septic tank discharging to ground through a drainage field was not affected: rule 5 for discharges to ground still requires treatment from a septic tank and infiltration system, which is the drainage field. What people call a soakaway for a septic tank is that drainage field, and it remains the standard arrangement.
What are the rules for a septic tank discharging to a soakaway or drainage field?
For discharges to ground under the general binding rules: 2 cubic metres a day or less (rule 1); treatment by a septic tank and infiltration system or a sewage treatment plant and infiltration system (rule 5); no pollution of surface water or groundwater (rule 4); not within groundwater source protection zone 1 or within 50 metres from any well, spring or borehole used for domestic or food production supply (rule 7). New discharges since 2 October 2023 have further siting conditions. If you cannot meet the rules you need an environmental permit; application fees are quoted at £117 for discharge to ground and £292 for discharge to a watercourse. Building Regulations add Approved Document H: 10 m from a watercourse or permeable drain, 15 m from a building, downslope of groundwater sources, no roads, drives, paving, water pipes or services over the disposal area.
What is the difference between a soakaway and a drainage field?
In the regulations, a soakaway for rainwater and a drainage field for sewage are different things. The general binding rules exclude a soakaway designed for draining rainwater installed after December 2007, and gov.uk defines a drainage field, also known as an infiltration system, as a series of pipes with holes placed in trenches. Approved Document H calls the sewage version a drainage field or drainage mound and describes it as perforated pipe in trenches on 300 mm of 20–50 mm stone, 500 mm below the surface, with 2 m of undisturbed ground between trenches. In Scotland SEPA uses the word soakaway for the sewage system itself, a sealed system of gravel filled trenches, and says it is sometimes referred to as an infiltration system. On a forum the usual advice is blunt: a rainwater soakaway for sewage is illegal, a drainage field designed to Part H is not.
What is a drainage mound and when do you need one?
A drainage mound is a drainage field built above the natural ground, in imported granular material, where trenches cannot work: slow percolation, a high water table, or bedrock close to the surface. Approved Document H gives its guidance for drainage fields and drainage mounds together in §1.26–1.44 and requires both to be designed to ensure aerobic contact between the liquid effluent and the subsoil; SEPA says a soakaway also includes mound soakaways, built above ground where percolation is slow or where digging trenches may be too difficult, for example where bedrock is close to the surface. A mound usually needs a pump: a Scottish self-builder whose own plot failed the percolation test got permission to put the soakaway under a higher neighbouring field, with a holding tank and submersible pump and 25 metres of 50 mm pipe up to it.
How close to groundwater can a drainage field be?
Not in it. Rule 4 forbids pollution of groundwater, Approved Document H requires the trial hole to be a minimum of 1 m² and 2 m deep, or 1.5 m below the invert of the proposed pipework, and says the groundwater table should not rise to within that depth; SEPA requires the highest seasonal water table, in winter, to be more than one metre below the base of the soakaway; and BS 6297 is reported to require that no part of the infiltration system be less than 1.2 metres above the highest predicted annual groundwater level. A consultant adds that the level must be measured in the wetter months because summer readings can be misleading. On clay, a DIYnot member describes the failure mode: the emptied tank refills through the outlet because the surrounding soil is waterlogged.
How big must the drainage field be?
Approved Document H gives the formula At = p × Vp × 0.25, where p is the number of persons served and Vp the percolation value in seconds per millimetre from the test in §1.34, valid only between 12 and 100. Four people on ground with Vp 40 need 40 m²; at a trench width of 600 mm that is about 67 m of trench, laid as a continuous loop fed from an inspection chamber, with trenches 300 to 900 mm wide and 2 m of undisturbed ground between them. On fast ground with Vp 12 the same house needs 12 m²; on slow ground with Vp 100, 100 m². Below 12 the effluent reaches groundwater too fast, above 100 it cannot soak away; outside the band a drainage field is not allowed, though a treatment plant with a soakaway may still be possible.
Researcher & editor, off-mains drainage
Writes independent guides on septic tanks, cesspits and sewage treatment plants for homes off the mains. Cross-checks the general binding rules and the Environment Agency, SEPA, NRW and NIEA against real prices, British Standards and what owners actually report on the forums.