Non return to sewer allowances

We know not all the water customers use will return to our sewers. As standard, we assume that customers return about 95% of their water back to our sewers. This is because around 5% of customers’ water either evaporates or is used during activities including drinking, cooking, car washing and watering plants and gardens.

If more than 5% of your water usage doesn’t return to our sewers, you could be eligible for a ‘non return to sewer’ allowance, which is a reduction in your sewerage charges. However, it’s important to note that the responsibility is yours as the applicant to evidence exactly how much water isn’t returning to the sewer and you need to prove this by measurement.

There is more information on the allowance and eligibility in the frequently asked questions below. After you submit the form at the bottom of this page, we will aim to respond within ten working days. We may ask for more information or visit your site to verify the claims.

Frequently asked questions

No, this is for foul water only. Surface water is rainwater that falls onto a property and runs from drainpipes, drives or paths into a drain or a road gulley into a public sewer. Foul water is water that usually comes from within buildings such as toilets, sinks, showers etc. The non return to sewer allowance is based on less than 95% of your foul water only not returning to our sewer. You can find out more information about our surface water rebate here, which is for properties where surface water does not drain into the sewer.

Any household or business customer who has a Welsh Water metered supply (i.e. a water meter) can apply. The main reasons for water not returning to the sewer are:

Evaporation (e.g. cooling towers, heated swimming pools, launderettes);
Irrigation (e.g. garden centres/golf clubs/sports grounds);
Removed off site (e.g. window cleaners, disposal off-site due to interceptor or tank cleaning);
Added to a product (e.g. cement works, food & drink manufacturers, livestock farms).

Uses such as jacuzzies, hot tubs, paddling pools, sprinklers and hosepipes are already covered in the standard 5% sewerage reduction. Businesses such as cafes, restaurants and take aways will not be eligible as this water will return to our sewers through toilet facilities.

As the responsibility is yours to evidence exactly how much water isn’t returning to the sewer, you need to calculate exactly how much water isn’t returning to the sewer and explain how you’ve calculated this. You also need to prove this by measurement, which could involve installing your own private sub meter and monitoring 12 months’ consumption. If sufficient information isn’t provided, we reserve the right to refuse the allowance.