Trade Effluent Consent | What Food Businesses Must Know

If you run a café, takeaway or restaurant in Windsor or the surrounding SL4 area, there's a letter from Thames Water you're supposed to have. Most food business owners I speak to have never heard of it. A few have heard of it and assumed it doesn't apply to them. Almost none of them have actually got one. That letter is a trade effluent consent, and ignoring it doesn't make the obligation go away.

Trade effluent consent is a legal requirement under the Water Industry Act 1991. If your business discharges anything into the public sewer beyond ordinary domestic-type wastewater, you need permission from your water company before that discharge happens. For food businesses, the culprit is almost always fat, oil and grease, collectively FOG, along with food particles, cleaning chemicals and sometimes sanitisers. All of that flows down your kitchen drain every single service. Thames Water covers Windsor and the surrounding villages, so they're the people you'd be dealing with.

Why most food businesses don't know about this

The consent requirement doesn't come with a reminder. There's no annual letter, no renewal notice, no pop-up on your business rates portal. When you open a café in Eton or take on a takeaway in Dedworth, nobody from the water company turns up to explain the paperwork. Environmental health officers deal with food hygiene. Your landlord deals with the lease. The drainage obligation falls through the gap.

The other reason it gets missed is that the consequences are invisible for a long time. Fat builds up in the sewer, slowly. Your kitchen drains fine for months, sometimes years, while a grease blockage grows downstream that eventually causes a sewage flood in someone's garden or a main sewer overflow. Thames Water traces it back. That's when the inspection happens.

What the consent actually covers

Applying for trade effluent consent means telling Thames Water what you're discharging, in what volume and at what times, and demonstrating that you've taken reasonable steps to prevent pollutants from entering the sewer untreated. For a food business, that means a functioning grease trap or grease interceptor, properly sized for your throughput, regularly serviced and with records to prove it.

Thames Water can impose conditions on your consent. Typical ones include:

• Maximum concentrations of FOG in your discharge (often 100mg per litre or lower)
• Mandatory grease trap installation and a maintenance schedule
• Record-keeping requirements so inspectors can see service dates and waste disposal
• Restrictions on what chemicals you can put down the drain

Breaching any condition is a criminal offence. The maximum fine for an unconsented trade effluent discharge is £1,000 per day under the Water Industry Act, but Thames Water can also pursue prosecution for causing or knowingly permitting pollution, where the fines are unlimited at Crown Court level.

The grease trap problem

Here's where I see things go wrong most often. A food business owner does get around to fitting a grease trap, usually because a plumber told them they needed one when they fitted the kitchen. The trap gets installed. Then it gets forgotten.

A grease trap that hasn't been emptied and cleaned on schedule does almost nothing. FOG fills the chamber, the trap loses capacity, and grease passes straight through into the drain as if the trap wasn't there. I've opened grease traps on commercial premises in the Spital and Clewer Village areas that were so solidified they needed mechanical descaling before we could even assess what size they were. That's not unusual.

Thames Water's inspectors know this. When a complaint about a sewer blockage leads them to a stretch of pipe serving a food business, the first thing they check is the grease trap: is it there, is it sized correctly, has it been serviced recently, and is there paperwork to prove it? An unmaintained trap with no service records is effectively evidence of a continuing breach.

For a small café doing maybe forty covers a day, a correctly sized passive grease trap typically needs emptying every four to eight weeks depending on throughput. A larger kitchen or a busy takeaway in Datchet or Windsor town centre might need it monthly or more. Your equipment supplier should give you a maintenance schedule. If they didn't, a CCTV drain survey downstream of your trap will tell you whether FOG is passing through.

What to do if you haven't got consent

Apply. Thames Water's trade effluent team handles applications, and the process involves submitting a notice describing your discharge before you make it. Yes, technically that ship has sailed if you've been trading for two years without one, but a retrospective application is far better than waiting for an enforcement visit.

Before you apply, get your grease management in order. Thames Water will want to know what you've installed and how you're maintaining it. If you've got a grease trap that's never been serviced, get it emptied, descaled and inspected now, and start a service log from that date. If your drains are already partially blocked with FOG, high-pressure water jetting will clear them, and a CCTV survey will show you whether there's damage further downstream.

Document everything going forward: service dates, the waste contractor you use to remove the grease, any repairs or replacements. That paper trail is your defence if an inspector ever turns up.

The practical side of staying compliant

Once you've got consent and a maintained grease trap, staying compliant isn't complicated. It's mostly about routine:

• Keep a physical service log next to the trap, not just a note in someone's phone
• Use a licensed waste carrier to remove grease waste, and keep their transfer notes
• Train kitchen staff not to pour cooking oil down the drain directly, even if it seems like a small amount
• Schedule a CCTV drain survey annually if you're a high-throughput kitchen, so you can see what's actually in your pipes before it becomes a blockage

The businesses that get into trouble are rarely the ones that made a deliberate choice to ignore the rules. They're the ones who didn't know, then assumed someone would have told them if it mattered, then gradually found the whole thing too complicated to address. Thames Water does pursue enforcement, and the fine plus the cost of an emergency drain clearance during a busy Friday service is considerably worse than the cost of a grease trap service schedule.

Drainsco covers Windsor and the SL postcodes, with engineers available around the clock. We handle commercial grease trap inspections, high-pressure jetting to clear FOG blockages, CCTV drain surveys, and drain relining where pipes have been damaged. There's no call-out fee, and you'll get a clear price before any work starts. If you're not sure whether your grease management is up to scratch, a camera survey is usually the quickest way to find out.