What the charge actually pays for

Your water bill isn’t really one number. It’s several separate charges stitched together: the clean water you use, the wastewater you send back, and a couple of charges for rainwater. Those rainwater charges are where the confusion tends to start.

There are two of them, and they get muddled all the time:

The word that matters for surface water is your. The charge assumes the rain landing on your buildings and hard surfaces runs straight into the public sewer, where it has to be carried away and treated. That holds up when it’s true. On a lot of commercial sites, though, it isn’t.

How the charge is calculated

Most wholesalers now charge surface water drainage in bands based on the total area of your site that could shed rainwater: roofs, yards, car parks and other hard surfaces. The larger that area, the higher the band, and the higher the charge. A few still base it on rateable value instead. Either way, each water company sets and publishes its own band thresholds in its annual charges scheme, so the exact boundaries vary by region.

The catch is that the band rests on an estimate of your hard-surface area rather than a measurement. An out-of-date or over-generous estimate is one of the most common reasons a site ends up a band or two too high, paying for drainage area it doesn’t actually have.

As a quick example, a distribution depot with a large warehouse roof and a couple of acres of yard would sit near the top of the banding, while a small high-street unit would sit near the bottom. If that depot’s yard actually drains to a soakaway rather than the sewer, it could be sitting in a high band for drainage it never uses.

To find where you sit, look at the surface water line on your bill and check it against your wholesaler’s published charges scheme. Every wholesaler issues one each year and they are public documents. The scheme sets out the band thresholds and rates, all approved by the industry regulator, Ofwat, under the Water Industry Act 1991. If the area you are billed for looks larger than your actual roofs and hard standing, that is the gap to challenge.

The fairest method, and the one the regulator Ofwat now favours, is charging by site area: the actual square metres of hard surface that drain to the sewer. Bands run from around 124 square metres at the smallest end up to several thousand at the top, with larger sites in higher bands. Yorkshire Water and Northumbrian Water have moved fully to site-area charging, and Severn Trent bills most of its business customers this way, replacing the older rateable-value approach that often bore little relation to how much a site actually drains.

Why so many businesses overpay

That word, estimate, is the heart of the problem. The whole charge rests on an assumption rather than a site visit, and nobody comes out to check where your water really goes. The wholesaler (your regional water company) sets the bands, and since the market opened up in 2017 your retailer just passes the charge along. So if it was wrong on day one, it stays wrong until someone questions it. The sites most likely to be overpaying tend to have one of these things in common:

• A big roof or car park that drains to a soakaway. Common on industrial units, depots, farms and retail parks.
• Rainwater that runs off to a stream or ditch instead of the sewer, often on riverside, rural and edge-of-town sites.
• A surface-area band that is set too high, where the estimated square metreage is bigger than the real thing.
• Sustainable drainage on site, such as permeable surfaces, ponds or swales that never made it onto the bill.
• A site that has been redeveloped, where buildings came down or surfaces changed but the charge carried on regardless.

One scope note. The deregulated market described here covers business premises in England, where you can also choose your retailer. Scotland opened its market earlier, in 2008, and works in a similar way. Most of Wales has not deregulated to the same extent, though the underlying surface water charge still applies and can still be challenged.

What counts as draining to the public sewer

To be charged surface water drainage fairly, your rainwater has to actually reach the public sewer. On a surprising number of sites it never does. It goes instead to a soakaway that lets it seep into the ground, straight to a watercourse like a stream or ditch, or into a sustainable drainage system (SuDS) such as a pond, swale or permeable surface.

It also helps to know how your area is drained. Older towns often have combined sewers that carry foul water and rainwater in the same pipe, while newer developments tend to have separate surface water sewers. If your rainwater enters either type of public sewer, the charge applies. If it stays out of the public system entirely, it shouldn’t.

Who pays on rented or leased premises?

On a tenanted commercial property the water bill, and the surface water drainage charge on it, is often in the landlord’s name, yet it’s usually the tenant who carries the cost through the lease or a service charge. That split is a big reason the charge goes unquestioned: the person paying it isn’t always the person who receives the bill.

If you lease your premises, check who holds the water account and what your lease says about recovering utility costs. A wrong surface water charge can be challenged whoever is named on the bill, and any refund should follow whoever actually bore the cost. On multi-let sites, the charge for shared yards and car parks can be apportioned in ways that repay a closer look.

How to tell if you’re being overcharged

Most of this is legwork rather than cost. The approach is the same either way: work out where your rainwater really goes, then compare that with what you’re being charged. If you’re paying for drainage you don’t use, you can ask for it to come off and be refunded.

1. Find it on your bill. Look for a line that says surface water drainage or just “surface water”, shown sometimes as a band and sometimes as a figure per square metre. Highway drainage usually sits right next to it.
2. Follow the water. Walk the site and trace your downpipes and yard gullies. Do they head for the public sewer, or off to a soakaway, ditch or drainage feature?
3. Get some proof together. Site plans, photos of soakaways or outfalls, or a quick drainage survey are the kind of evidence a water company will accept.
4. Ask for the charge to come off. The request goes to the wholesaler, usually through your retailer, to reclassify the site or move you to a lower band.
5. Claim it back. If the charge was wrong, it was wrong for years. Most wholesalers will refund past overpayments, usually up to six years, the limit set by the Limitation Act 1980.

Claims usually only stall for a few reasons: the site does connect to the public sewer after all, the evidence doesn’t clearly show where the water goes, or the drainage is mixed and the split can’t be demonstrated. Solid evidence is what gets a claim over the line, which is why a short drainage survey often pays for itself.

A drainage survey is simply a specialist tracing where the water from your downpipes and gullies ends up, often using dye or a small camera, and producing a plan that shows it. That plan is the proof a wholesaler wants to see, and it tends to be a modest, one-off piece of work rather than a major undertaking.

You can work through this yourself. If you’d rather not, a business water audit will check whether your surface water drainage charge is correct, and flag anything else on the bill that looks off, so nothing slips through. It’s the same process, done for you.

As for timing, the process takes a little patience. A straightforward reclassification might be settled in a few weeks, while a larger claim with a backdated refund can take a few months, as the wholesaler reviews the evidence and recalculates past bills. It helps to note the date you applied and to chase if things go quiet.

Can you remove the charge for good?

Reclassifying your site lowers or removes the charge on paper. There’s also a more permanent route: physically disconnecting your rainwater from the public sewer. Reroute your downpipes and gullies to a soakaway, a watercourse or a sustainable drainage system, and your site stops using the sewer for surface water altogether, so the charge can come off for good.

It’s a bigger step, involving drainage work and the right permissions, so it tends to suit larger sites where the ongoing charge is significant, or where drainage is being upgraded anyway. For most businesses, correcting an inaccurate band or proving existing drainage to a soakaway is enough on its own. Either way the starting point is the same: knowing exactly where your rainwater goes.

Surface water drainage FAQs

Related terms: Highway drainage  ·  Pence per cubic metre