Excellent 5* RatingBusiness Water Glossary
What is a return to sewer allowance?
Your sewerage bill is usually worked out on the assumption that nearly all the water you buy goes straight back down the drain. A return to sewer allowance is the adjustment you can claim when that isn’t true, when a chunk of your water never reaches the sewer at all.
For the right kind of site, it’s one of the simplest ways to get a water bill down.
What a return to sewer allowance is
When you’re billed for wastewater, the water company doesn’t actually measure what leaves your site. It assumes a set percentage of the clean water you buy comes back to the public sewer, and bills your sewerage charge on that basis. A return to sewer allowance trims that charge to reflect water that genuinely doesn’t come back. It only touches the wastewater side of the bill, not the clean water you’ve used.
How sewerage charges normally work
The standard assumption across the industry is that 95 per cent of the water you buy comes back to the sewer. Put another way, a 5 per cent non-return is already built into most bills, which covers the small everyday losses: water that gets drunk, used in cooking, or simply evaporates. You only need to claim an allowance when more than 5 per cent of your water genuinely doesn’t reach the sewer.
For an ordinary office, that 95 per cent assumption is about right. For sites that use water in other ways, it can be miles off, and you end up paying to dispose of water the sewer never sees. The return figure and the way allowances are handled are set out in each wholesaler’s charges scheme, signed off by the regulator, Ofwat, so the finer detail shifts a little from region to region.
When you can claim
You can apply when a real, measurable share of your water doesn’t go back into the sewer, beyond that built-in 5 per cent. The usual culprits:
- Water that ends up in a product. Food, drink, concrete or cosmetics that leave site carrying the water with them.
- Irrigation and landscaping. Watering crops, pitches or grounds.
- Evaporation. Cooling towers, laundries and leisure sites that lose water to the air.
- Vehicle or plant washing where the water drains away off-site or to a soakaway.
- Top-up water for ponds, tanks or processes that never discharge.
How the allowance is worked out
An allowance is really just a water balance: the water coming onto your site set against the water that actually returns to the sewer. Whatever doesn’t return is what the allowance is based on, and it lands on your bill as a percentage taken off the sewerage charge.
The burden of proof sits with you. Wholesalers expect you to show, by measurement, that materially less than 95 per cent comes back, so the cleaner route is a sub-meter on the non-returning supply, often monitored across a full 12 months to capture seasonal swings. Where metering isn’t practical, an agreed calculation built from your process or production figures can stand in. The stronger your evidence, the smoother the claim.
How to claim an allowance
The process is simple enough, but it leans on evidence of how much water doesn’t come back:
- Pin down the non-returning water. Work out which parts of your process use water that never reaches the sewer, and roughly how much.
- Measure it. A sub-meter on the relevant supply gives a clean number, ideally over a full year. If metering isn’t practical, an agreed calculation from your process does the job.
- Apply through your retailer. They put the case to the wholesaler, who agrees the allowance.
- Agree the percentage. Once it’s accepted, your sewerage charge drops by the allowed share from then on.
- Claim it back. If you’ve been over-charged because the standard assumption didn’t fit, the adjustment can usually be backdated up to six years, the limit set by the Limitation Act 1980.
Return to sewer allowance, or trade effluent?
These two get mixed up constantly, and they’re really opposites. A return to sewer allowance is for water that doesn’t reach the sewer. Trade effluent charges are for process water that does reach the sewer and needs treating.
| Return to sewer allowance | Trade effluent | |
|---|---|---|
| Applies to | Water that never reaches the sewer | Process water that does reach the sewer |
| Effect on the bill | Reduces your sewerage charge | Adds a charge for treating the discharge |
Plenty of sites have a bit of both, so it’s worth checking which one applies where. Our guide to trade effluent covers the other side of it.
Return to sewer allowance FAQs
What is a return to sewer allowance?
It’s a reduction to your sewerage charge that reflects water you buy but don’t return to the public sewer, for example water that goes into a product or evaporates.
What is the standard return to sewer assumption?
Most water companies assume 95 per cent of the water you buy returns to the sewer, so a 5 per cent non-return is already allowed for. You claim a return to sewer allowance when more than 5 per cent doesn’t come back.
Who qualifies for one?
Any business where a real, measurable share of its water doesn’t reach the sewer beyond that 5 per cent. Manufacturers, food and drink producers, laundries, car washes, farms and leisure sites are common examples.
Do I need a sub-meter to claim?
Usually it helps. The burden of proof is on you, so a sub-meter on the non-returning supply, often monitored over 12 months, is the cleanest evidence. An agreed calculation can work where metering isn’t practical.
Can it be backdated?
Often, yes. Many wholesalers will backdate the adjustment up to six years, the period set by the Limitation Act 1980, though it’s worth confirming when you apply.
Is it the same as a trade effluent allowance?
No. A return to sewer allowance is for water that doesn’t reach the sewer at all. Trade effluent charges apply to process water that does reach the sewer.
Does a return to sewer allowance reduce my whole bill?
No. It only reduces the sewerage, or wastewater, part of your bill, which is based on how much water is assumed to return to the sewer. Your clean water charges are unaffected.
Which businesses benefit most?
Water-intensive sites where a lot of water leaves another way: food and drink producers, breweries, car washes, nurseries and farms, and anywhere with significant evaporation, such as laundries and leisure facilities.
Related terms: Pence per cubic metre · Highway drainage
Think water is leaving your site another way?
A business water audit can check whether a return to sewer allowance applies, and whether there’s money to come back.
