Who regulates septic tanks in Cornwall?
Cornwall is in England, so private sewage discharges are regulated by the Environment Agency. In England, small sewage discharges (up to 2 m³ a day to ground, or 5 m³ a day to surface water) don't need a permit if they meet the general binding rules. Under those rules, septic tanks must not discharge to surface water such as a ditch or stream, systems must meet the relevant British Standard and be sized correctly, and new discharges can't be in or within 50 metres of protected sites or in Source Protection Zone 1. Any new septic tank or treatment plant needs building regulations approval.
Building approval for a new or replacement system comes from Cornwall Council building control or a registered building control approver. Read more in our England regulations guide.
Ground and soil conditions
Granite uplands, such as Bodmin Moor, Carnmenellis and West Penwith, have shallow, acidic soils. Much of the rest of the county is 'killas', slates and mudstones that can drain unevenly. Cornwall's mining legacy means old shafts and workings are possible on some sites, and a mining search is sensible before you dig.
Protected waters and environmental checks
Cornwall has a lot of bathing waters, shellfish waters and protected estuaries, such as the Fal and Helford and the River Camel. The general binding rules don't allow septic tank discharges to surface water, and new discharges near protected sites need a permit.
Local practicalities
Holiday lets are very common. A property that sleeps more people in summer needs a system sized for its peak occupancy using British Water's Flows and Loads guidance, not the usual household figures.
Towns and villages covered
Installers we work with cover Cornwall, including:
- Truro
- Bodmin
- Launceston
- Liskeard
- Helston
- Penzance
- St Austell
- Wadebridge
- Bude
- Camelford
- Redruth
- Callington
The list isn't exhaustive. Enter your postcode and we'll find installers who cover your property.
What it typically costs
The figures below are national guide prices from installers' published guides and merchants' list prices, because there's no reliable published data for Cornwall on its own. Expect your quote to reflect the local ground, access and discharge route described above.
- Like-for-like septic tank replacement: roughly £3,000–£7,000
- New septic tank with drainage field: from about £5,500; commonly £5,000–£15,000
- New drainage field: £3,000–£7,000
- Sewage treatment plant unit only: about £2,190–£2,700 inc VAT (equipment only)
- Sewage treatment plant, supplied and installed: commonly £7,500–£15,000
- Emptying: priced by volume. One private tanker firm charges £170 for up to 1,000 gallons and £380 for up to 4,000 gallons
Other areas in England
Norfolk · Suffolk · Lincolnshire · Devon · Cumbria · North Yorkshire · Northumberland · Shropshire · Herefordshire · Somerset · Dorset
Frequently asked questions
We let our property as a holiday home. What size treatment plant do we need?
It's sized on maximum occupancy and use, following British Water's Flows and Loads guidance, not on the number of bedrooms alone. Give installers your maximum guest numbers and any extra facilities, such as a hot tub or laundry.
Do I need a mining search before installing a drainage field?
It's sensible in mining areas. A Cornwall mining search can flag old shafts or workings near where you plan to dig.
How much does septic tank replacement cost in Cornwall?
We don't publish made-up local prices. Installers' published guides put a like-for-like replacement at roughly £3,000–£7,000, a new tank with a drainage field at commonly £5,000–£15,000, and a treatment plant at commonly £7,500–£15,000 fitted. Ground and access in Cornwall can move your price either way, so compare site-visit quotes.