Why drainage charges catch businesses out

Drainage charges aren’t based on usage alone

Unlike your volumetric water charges, drainage fees are usually based on property characteristics rather than consumption. Surface water drainage charges cover rainwater that runs off your roof, yard, car park or other hard surfaces into the public sewer. In many cases, highway drainage charges are also included, covering the cost of removing rainwater from public roads.

This means your bill isn’t purely about operational water use. It’s also about the physical footprint of your premises. If your site has a large roof area or extensive hardstanding, that can increase the drainage element regardless of how carefully you manage your water consumption inside the building.

We often find that this is where frustration starts. You may have invested time and effort into reducing usage, only to see a limited impact on the total bill because drainage charges remain unchanged. However, when you understand how these costs are calculated, the numbers begin to make more sense.

Charges are sometimes calculated using estimates

In many cases, drainage charges are calculated using mapping systems, historic property data or estimated surface areas. Suppliers don’t usually visit every site to measure drainage in person. Instead, they rely on aerial imagery and database records to assess how much of your property drains into the public sewer.

That approach works in principle, but it isn’t flawless. If your site has been extended, altered or partially redeveloped over time, the recorded surface area may not reflect reality. We’ve seen situations where areas that don’t drain into the public sewer are still included in the chargeable calculation.

If you’re reviewing your bill and something feels disproportionately high compared to the size or layout of your site, it’s worth questioning. Assumptions made years ago can remain on an account indefinitely unless someone actually takes the time to check them.

Some businesses are charged when they shouldn’t be

One of the most common issues we come across is businesses paying for surface water drainage when their rainwater doesn’t enter the public sewer at all. If your site drains into a soakaway, a sustainable drainage system or a nearby watercourse, you may not be liable for certain surface water charges.

Many businesses simply accept what’s on the invoice because it comes from a regulated supplier. Understandably, you assume it’s correct. However, drainage classifications aren’t immune to error. If no one has ever reviewed how your site actually drains, there’s a chance the account is set up on an assumption rather than confirmed details.

If you’re the one handling utilities for your business, this is an area that’s well worth double-checking. Even a small adjustment to the drainage element can have an ongoing impact on your annual costs.

Drainage costs aren’t always clearly explained

Business water bills aren’t always easy to interpret. Drainage charges may appear as separate line items, be bundled with wastewater charges, or sit within standing charges, depending on your supplier and region. There isn’t a single, consistent format across the market.

That inconsistency can make it difficult to compare like-for-like. If you’re trying to benchmark costs across sites or assess whether a bill looks reasonable, that, along with unclear presentation, adds another layer of complexity. It also means drainage can quietly sit in the background for years without ever being reviewed.

When we look at our customers’ accounts, one of the first things we do is break down exactly what each element represents. Once it’s laid out clearly, it becomes much easier to see what you’re paying for and whether it aligns with how your premises actually operate.

Reviewing drainage charges supports better cost control

As the person responsible for water in your organisation, you’re likely tasked with keeping costs controlled and avoiding unexpected increases where possible. Keeping an eye on your drainage charges isn’t just about spotting errors. It’s about understanding the full structure of your bill, so you’re not caught off guard later.

When you understand every charge on your bill and where it comes from, you have a far clearer picture of your true baseline costs. That makes budgeting easier and reduces the risk of sudden queries from finance when a bill looks higher than expected.

It also puts you in a stronger position if you decide to switch business water suppliers. When your site details and drainage classifications are correct, quotes are based on reliable information. That means fairer comparisons and fewer surprises after a switch.

How to check whether your drainage charges are correct

Start with your latest bill. Look for any reference to surface water drainage or highway drainage. Make a note of how it’s described and how it’s being charged. Then compare that to how your site actually drains. Does rainwater flow into the public sewer, or does it go elsewhere?

If you’re unsure, site plans, facilities managers or landlords can often provide more information. Even a visual inspection of guttering and drainage points can offer useful insight. The important thing is to match what happens on the ground with what’s reflected in the account.

If you find there’s a mismatch, it’s worth raising the question. A review doesn’t automatically mean something is wrong, but it does make sure your bill reflects your real-world setup.

If you’re unhappy with your current provider and feel you aren’t getting value for money, it might be time to switch business water suppliers. At The Business Water Shop, we review your existing charges in detail, check that your drainage, tariffs and account details are accurate, and then compare the market to help you secure the most cost-effective option for your business.
Simply head to the ‘compare now’ section of our website and fill out the form. It only takes a few moments to compare the latest 2026 business water rates, and you’ll quickly see whether you could be paying less and exactly where you stand.