Surface Water Drainage Rebates: How to Check and Claim

Surface water drainage is one of the least understood lines on a business water bill, and one of the most frequently wrong. It is also unusual in that when it is wrong, you may be able to get money back rather than simply pay less going forward.

Surface water drainage is a charge for rainwater that falls on your premises and drains into the public sewer. It is normally estimated from the area of your site rather than measured, so if your rainwater actually goes to a soakaway, a watercourse or a private drain, you may be paying for a service you never receive — and a successful claim can often be backdated.

This guide explains what the charge is, how to check your own site, and how to go about claiming.

What is surface water drainage?

When rain falls on a roof, yard or car park it has to go somewhere. If it runs into the public sewer network, the wholesaler has to convey and treat it, so it levies a charge. Because nobody meters rainwater, that charge is calculated from an assumption: typically the area of your site, or a band based on it.

That assumption is where the problem starts. Site records can be decades old, they are rarely revisited when a building changes use or is extended, and they take no account of drainage that bypasses the public sewer altogether. The charge sits on the bill year after year and almost nobody questions it.

Why do so many businesses overpay?

There are four common situations where the charge is wrong:

• The rainwater never reaches the public sewer. Many industrial and rural sites drain to a soakaway, an attenuation pond, a private system or directly to a watercourse. If none of your surface water enters the public sewer, there is no service being provided.
• Only part of the site drains to the sewer. A partial rebate is still a rebate. It is common for a building's roof to be connected while a large yard or car park drains elsewhere.
• The recorded site area is wrong. Charges based on an out-of-date plan, or on the whole of a site you only partly occupy, overstate the charge.
• You are billed for land you do not control. Shared estates and subdivided buildings frequently produce duplicated or misallocated charges.

How to check your own site

You can do a credible first assessment yourself in an afternoon:

1. Find the charge on your bill. Look for a line described as surface water drainage, highway drainage or similar. If you cannot see one, ask your retailer to confirm whether it is included and how it is calculated.
2. Establish the area you are being charged for. Your retailer or wholesaler should tell you the figure they hold. Compare it with your actual demise.
3. Walk the site and follow the water. Note every gully, downpipe and drain. Where does each one go? Soakaways, ponds, ditches and watercourses all point away from the public sewer.
4. Get evidence together. A site plan marked with drainage runs, photographs of the outfalls, and any drainage or planning drawings you hold will all support a claim.
5. Check for a highway drainage element. Some wholesalers charge separately for road drainage, which may not apply if your access is private.

If a drainage survey is needed to prove the case, weigh the cost against the size of the charge and the number of years potentially recoverable.

How to claim a rebate

Claims are made to your water retailer, who takes it up with the regional wholesaler. In practice that means submitting your evidence, waiting for the wholesaler to assess it, and, if accepted, having the charge removed or reduced going forward with a credit for past years.

How far back a claim can go is set by the wholesaler's own policy rather than by a single national rule, so it varies. That is precisely why it is worth checking sooner rather than later — every year that passes is potentially a year you cannot recover.

Two practical points. First, keep the claim factual and evidenced; assertions without drawings rarely succeed. Second, be prepared for it to take time, because the wholesaler may want to verify the drainage arrangement itself.

Which businesses should definitely check?

Any site with a large outdoor footprint relative to its water use is worth a look. In our experience that means industrial units and warehouses with big yards, farms and rural premises, garden centres, car parks and forecourts, self-storage, and any site on a former industrial plot where drainage was built long before the current occupier arrived.

It is also worth checking if you have recently taken on a site, extended a building, or changed how part of the premises is used, since none of those changes reliably make their way into the charging records.

Frequently asked questions about surface water drainage

What is surface water drainage on a water bill?

It is a charge for rainwater falling on your premises that drains into the public sewer, where the wholesaler has to convey and treat it. It is normally estimated from the area of your site rather than metered.

Can I get a surface water drainage rebate?

Yes, if you can show that some or all of your rainwater does not enter the public sewer, or that the site area used to calculate the charge is wrong. Claims are submitted through your water retailer to the regional wholesaler with supporting evidence.

How far back can a surface water drainage rebate be backdated?

It depends on the wholesaler, as each sets its own policy on retrospective credits rather than there being one national rule. Because the recoverable period is limited, checking earlier gives you a better chance of reclaiming more.

What evidence do I need for a drainage claim?

A site plan showing where each drain runs, photographs of the outfalls, and any drainage or planning drawings you hold. The stronger the documentary evidence that rainwater bypasses the public sewer, the more straightforward the claim.

Not sure whether you are paying it?

Send us a recent bill and we will tell you whether a surface water drainage charge is on it, how it has been calculated and whether it looks challengeable. It is one of the first things we check on any business water review. You can also read our guide to what business water actually costs, our guide to trade effluent consent, or see the full range of services we offer. Call 0151 541 6767 if you would rather talk it through.