What counts as trade effluent?

Trade effluent is any liquid waste from a business or industrial process that drains to the public sewer, anything beyond ordinary domestic sewage or clean rainwater. If your premises send something other than normal toilet and washroom wastewater down the drain, it’s very likely trade effluent.

It shows up across a lot of sectors:

• Food and drink production. Washdown, processing water, brewing and distilling.
• Commercial laundries. Detergents, fibres and warm water at volume.
• Vehicle washing. Car washes and fleet cleaning, carrying silt and oils.
• Manufacturing and metal finishing. Process water, cooling and surface treatment.
• Print, chemical and cosmetic production. Anything that rinses product residue to drain.

The distinction matters, because each kind of wastewater is charged in its own way:

The consent you need to discharge it

Before you can put trade effluent into the sewer, you need a trade effluent consent from your wholesaler, the regional water company, under the Water Industry Act 1991. It’s a legal requirement, not a box-ticking exercise.

The consent sets limits on what you’re allowed to discharge, and it usually covers:

• Volume and flow rate. How much you can discharge, and how quickly.
• Strength. Measured as chemical oxygen demand and suspended solids.
• Temperature and pH. Keeping the effluent within safe limits for the sewer.
• Specific substances. Limits on metals, oils and certain chemicals.

It’ll normally come with conditions too, like regular sampling and metering. Discharging without a consent, or going outside the one you hold, is a criminal offence, so it’s worth checking your consent still matches what your site actually puts down the drain today, rather than what it discharged when the consent was first granted.

One to watch: some discharges count as “special category” effluent, where the substances involved bring the Environment Agency into the picture alongside the wholesaler. If your process uses anything unusual, check early whether it falls into that bracket.

The application itself is fairly detailed, covering the volume, the nature of the effluent and the substances it contains. Once a complete application is in, the wholesaler usually has two months to decide, and longer if new treatment or infrastructure is needed. For special category effluent, the wholesaler can’t issue consent until the Environment Agency has reviewed it and either refused it or set the conditions, so those cases take longer.

How trade effluent is charged

Trade effluent charges are worked out using the Mogden Formula, which prices your discharge on how much there is and how strong it is. The more you discharge, and the dirtier it is, the more you pay. In plain terms, three things drive the charge:

The charge also covers carrying the effluent away, treating it and dealing with the leftover sludge. Because it’s built on strength, it reacts directly to what you put down the drain, and that’s exactly what makes it something you can influence.

“Strength” isn’t a single number. It’s measured mainly as chemical oxygen demand, the organic load, taken after the effluent has been left to settle, and suspended solids, the solid matter it carries. Your figures are then set against an average, or standard, strength for ordinary sewage, and the further above that standard your effluent sits, the more each unit costs. Some wholesalers are now also starting to charge separately for ammoniacal nitrogen, which the formula has traditionally left out.

Your effluent’s strength is established by sampling. If your charges are based on a cautious assumed strength rather than recent samples, that’s often where overpayment creeps in, and it’s something you can ask to have re-checked.

One point in your favour: trade effluent charges are zero-rated for VAT, the same as the rest of your wastewater charges. That holds even if your business sits in an industrial sector that pays standard-rate VAT on the clean water it uses, so if you ever see VAT on a trade effluent line, it’s worth querying.

How to reduce your trade effluent charges

Because the charge follows volume and strength, there are some practical ways to bring it down:

1. Measure what you actually discharge. A meter or a round of sampling shows your real volume and strength, which is often lower than the assumption your bill is based on.
2. Screen and settle out the solids. Taking suspended solids out before the effluent leaves site drops both the solids and the organic load.
3. Pre-treat where it pays. On-site treatment can cut the strength enough to move you to a lower charge.
4. Use, and reuse, less water. Less water through the process means less effluent out, and a smaller volume charge.
5. Keep your consent current. A consent that matches your real discharge keeps you out of breach and stops you paying against worst-case assumptions.

If you’d rather not work through it in-house, a business water audit can look at your discharge, your consent and your Mogden charges together and point to where the savings are.

Who’s responsible, and who pays?

The consent sits with the occupier who actually makes the discharge, so on most sites that’s the business operating there rather than the landlord. If you lease your premises, it’s worth being clear in the lease about who holds the consent and who carries the charges, because the two aren’t always the same party.

It really matters when something changes. If you take on a site, alter your process, or inherit a consent that no longer fits what you do, putting it right falls to you as the current discharger. A quick check of the consent when you move in, or when you change a process, saves a lot of trouble down the line.

Discharging to a sewer or a watercourse?

Trade effluent consents are about discharging to the public sewer. If your effluent goes somewhere else instead, to a watercourse like a river or stream, or to ground, that’s a different regime: it needs an environmental permit from the Environment Agency (or Natural Resources Wales in Wales), not a trade effluent consent from your water company.

The difference is easy to miss but important, because the wrong permission, or none at all, is an offence either way. If you’re not sure where your effluent actually ends up, tracing it is the first thing to sort.

Trade effluent FAQs

Related terms: Highway drainage  ·  Pence per cubic metre Mogden formula