Do UK commercial kitchens legally need a grease trap? No single statute says “fit a grease trap” in those words, but three overlapping rules make grease management a legal reality for any premises cooking hot food. Section 111 of the Water Industry Act 1991 makes it a criminal offence to discharge anything into a public sewer that is likely to interfere with the free flow of its contents, which describes fat, oil and grease precisely. Approved Document H of the Building Regulations says drainage serving commercial hot-food kitchens should have a grease separator or other effective means of grease removal. And water companies inspect food businesses and prosecute persistent offenders. So the practical answer is yes: a kitchen producing meaningful amounts of fat, oil and grease (FOG) needs to keep it out of the sewer, and a correctly sized trap or separator is the standard way to show it. None of this is legal advice: always check your lease, any trade effluent consent and your water company’s own requirements.
What FOG does once it leaves your sink
Hot cooking fat flows down a plughole without complaint. In the sewer it cools, hardens and bonds with wipes and food solids into deposits that eventually seal the pipe, and sewers are shared, so your discharge combines with every other kitchen’s on the same run. At scale the result is the fatberg: Thames Water reports that FOG is linked to more than 20,000 sewer blockages across its region each year, over 60% of sewer flooding incidents, and around £40 million in annual costs. That bill is why these rules are increasingly enforced at the kitchen door.
Where the legal duty comes from
Section 111, Water Industry Act 1991. The offence is throwing, emptying or allowing to pass into a public sewer “any matter likely to injure the sewer or drain, to interfere with the free flow of its contents or to affect prejudicially the treatment and disposal of its contents”. Congealed grease interferes with free flow by definition. On summary conviction the penalty is a fine plus a further daily fine if the offence continues after conviction; on indictment, up to two years’ imprisonment, a fine, or both. The section never mentions grease traps; it simply makes unmanaged grease an offence and leaves you to choose the equipment that prevents it.
Building Regulations, Approved Document H. Paragraph 2.21 of the 2015 edition states that “drainage serving kitchens in commercial hot food premises should be fitted with a grease separator complying with BS EN 1825-1:2004 and designed in accordance with BS EN 1825-2:2002 or other effective means of grease removal”. Approved Documents are guidance rather than law, applied when a kitchen is built or materially altered, so an older kitchen is not automatically in breach. But it sets the benchmark building control expects, and “other effective means” must genuinely be effective.
Trade effluent consents. A food manufacturer or large processing kitchen discharging trade effluent needs the water company’s consent, and breaching its conditions is prosecutable in its own right, as the cases below show.
Who enforces it, and what happens when they do
The sewerage undertaker polices its own network, and across this part of the country that means Thames Water. Its Network Protection Team made more than 19,000 visits to food businesses across London and the Thames Valley in a year, leading to the installation of more than 2,500 fat traps. Its stated position: food businesses “are required to ensure they have effective grease management measures in place”, a basic fat trap is not enough if it does not actually achieve compliance, and inspectors return to check equipment is maintained and working.
Education comes first, not indefinitely. In two prosecutions announced in late 2024, Kolak Snack Foods Limited was fined £152,000 plus costs at Willesden Magistrates Court for discharging effluent containing food solids and fats in breach of its consent, and Taiko Foods Limited £88,500 plus costs for 13 offences including putting chemicals, solids and fats into the sewers. Over £260,000 in fines and costs between two companies is the current price of treating the sewer as a disposal route. Environmental health officers pay attention too, since a backing-up drain in a food premises is a hygiene problem as well.
What counts as grease management
A trap or separator sized to the kitchen. A passive grease trap under the pot wash, or a larger separator outside, gives wastewater time to cool so grease floats and solids sink, with cleaner water carrying on to the sewer. Sizing is the part that gets skipped: BS EN 1825-2 covers selecting the nominal size as well as installation and maintenance, and an undersized trap passes grease straight through and proves nothing.
Dosing systems, within their limits. Biological and enzyme dosing units break grease down in the pipework. They can help keep internal runs clear, but they are a supplement rather than a substitute: incompletely broken-down grease can re-form further along the network, which is precisely what enforcement targets. A dosing unit alone, with no separation and no records, is a hard position to defend at an inspection.
Kitchen practice. Dry-wiping pans into the bin before washing, strainers in every sink, and staff who know why both matter.
Used cooking oil is a separate duty. Fryer oil never belongs in any drain, trap or no trap. Food Standards Agency guidance requires waste cooking oil to be stored securely and taken by an authorised collector to an authorised site for recovery or disposal; it cannot go in the general waste either.
The paperwork: duty of care and Waste Transfer Notes
Grease trap waste is business waste, so the moment it leaves your premises the duty of care rules apply. You must store waste safely, check that whoever takes it away is a registered waste carrier, complete a Waste Transfer Note for each load, and keep your copy for two years, ready to show a council or Environment Agency officer. The carrier check takes two minutes on the Environment Agency’s public register, and an unregistered collector who tips your trap waste in a layby leaves you holding part of the liability. Those dated notes double as your compliance record: the simplest evidence a water company inspector, an EHO or a landlord could ask for.
How often should a grease trap be emptied?
There is no statutory interval, and any firm quoting one universal frequency is guessing. It depends on the trap’s capacity against the kitchen’s output: a fryer-heavy takeaway fills a small under-sink trap many times faster than a sandwich café fills a large external separator. BS EN 1825-2 ties maintenance to the installation’s size and use, and the working rule is to empty before the trap loses effectiveness rather than after. Smell, slow drainage at the sinks it serves, and grease visible in downstream chambers all say the interval is too long.
Landlords, leases and franchises
Most commercial leases require the tenant to comply with statute and keep the drains serving the premises clear, and many food-premises leases or franchise agreements name grease management specifically. A blocked shared stack in a parade of shops quickly becomes a dispute about whose fat caused it, and dated maintenance records resolve that far more cheaply than solicitors.
Where TrueFlow fits in
TrueFlow handles the maintenance side of FOG compliance for kitchens and restaurants across Berkshire and the surrounding counties: grease trap emptying and cleaning with a Waste Transfer Note issued for every collection, as an Upper Tier registered waste carrier (registration CBDU538687). Scheduled drain jetting from £150 including VAT keeps grease-loaded stacks clear between trap services, timed for hours you are closed, and the wider commercial drainage service covers gullies, interceptors and external pipework. Site surveys are free, the exact price is agreed before any work starts, every visit carries insurance and a 6-month guarantee, and the phone is answered 24/7, 365 days a year with a 60-minute emergency response target. Published prices are on the pricing page.
Grease trap and FOG rules FAQs
Do UK commercial kitchens legally need a grease trap?
No single law orders every kitchen to fit a grease trap, but the combined effect of the rules makes grease management compulsory in practice. Section 111 of the Water Industry Act 1991 makes discharging matter likely to interfere with sewer flow a criminal offence, Approved Document H of the Building Regulations expects grease separation in commercial hot-food kitchens, and water companies require effective grease management. A correctly sized trap or separator, emptied regularly with records kept, is the standard way to comply.
Is it illegal to pour fat down the drain in the UK?
For a business, effectively yes. Under section 111 of the Water Industry Act 1991 it is a criminal offence to discharge anything into a public sewer likely to interfere with the free flow of its contents, and congealed fat, oil and grease does exactly that. Penalties range from fines to two years’ imprisonment on indictment.
How often does a grease trap need emptying?
There is no legally fixed interval. Frequency depends on trap capacity against kitchen output: a small under-sink trap in a busy frying kitchen may need emptying every few weeks, while a generous separator in a light-use kitchen lasts much longer. BS EN 1825-2 links maintenance to the installation’s size and use. Empty before the trap loses effectiveness, and treat smells, slow sinks or grease in downstream chambers as signs it is overdue.
What paperwork do I need when my grease trap is emptied?
A Waste Transfer Note for every collection, kept for two years, under the waste duty of care. It records what the waste is, where it came from and who took it; both parties sign. You must also check the collector is a registered waste carrier on the Environment Agency’s public register. The file of notes also serves as evidence of a maintained trap.
If your kitchen needs a trap emptied, a greasy stack jetted or an honest view of whether the current setup would survive an inspection, call TrueFlow on 0808 175 7440 or book a free site survey. The compliance paperwork comes with every visit, not just the clean drain.