What Are Surface Water Drainage Charges?

Every time it rains, water runs off roofs, car parks and yards. On many business sites that rainwater flows into the public sewer, and the water company charges for dealing with it. This is the surface water drainage charge. It often sits quietly on the bill, but it is worth understanding – particularly if your rainwater goes somewhere else.

Key takeaways

• Surface water drainage charges cover rainwater from your property entering the public sewer.
• Charging methods vary between water companies.
• If no rainwater from your site reaches the public sewer, you may be able to apply for a rebate.
• Evidence of where your rainwater goes is key.
• Sites with several premises should check each one separately.

What the charge covers

Surface water drainage is the cost of collecting and dealing with rainwater that runs off your property into the public sewer network. It is separate from foul sewerage, which covers water from toilets, sinks and kitchens. For business customers in England, the charge is passed on by the wholesaler to your retailer, which then bills you.

How it is calculated

There is no single national method. Depending on the wholesaler, surface water drainage may be charged:

• By site area – based on the size of the property, sometimes in bands.
• By meter or supply pipe size – used as a proxy for the size of the site.
• As a fixed charge – for certain property types.

Methods also change over time. Southern Water, for example, has set out plans to move its business surface water charges from a pipe-size basis towards a site-area basis. If your wholesaler's method changes, it is worth checking that the information used about your site is correct.

When you may not need to pay

If none of the surface water from your property enters the public sewer, you may be able to apply for a rebate or have the charge removed. This could be the case if rainwater drains to:

• A soakaway on your land.
• A river, stream or ditch.
• A private drainage system that does not connect to the public sewer.

Water companies set their own conditions. Welsh Water, for example, says on its surface water rebate page that you only qualify if no surface water enters its network, that partial drainage does not qualify for a reduction, and that a water butt does not count because it is not a permanent fixture. Thames Water's surface water drainage guidance says rebates require supporting evidence and can be backdated for up to six years. Other companies' rules may differ.

Partial drainage

Many business sites have mixed drainage – the roof drains to a soakaway but the car park drains to the sewer, for example. Some wholesalers may offer reduced charges in these cases; others, like Welsh Water, say partial drainage does not qualify. Check your wholesaler's current scheme.

How to find out where your rainwater goes

1. Look at site drawings from when the building was built or extended.
2. Check property records such as drainage searches from when you bought or leased the property.
3. Walk the site and follow gutters and downpipes to see where they lead.
4. Ask your landlord or managing agent if you lease the premises.
5. Consider a drainage survey if records are unclear. A specialist can trace connections with dye tests or cameras.

How to apply for a rebate

For business customers in England, your retailer is usually your first point of contact, and it will liaise with the wholesaler. In Wales, most business customers deal directly with Dŵr Cymru Welsh Water or Hafren Dyfrdwy. The process generally involves:

• Completing an application or providing a written request.
• Supplying evidence such as drainage plans or survey results.
• Allowing a site visit if the water company asks for one.

Keep paying your charges while the application is assessed. If the rebate is approved, the water company will explain what credit, if any, applies to past periods.

Common reasons charges may be wrong

• The site was recorded as connected when it never was.
• Drainage was altered – for example a new soakaway – but records were not updated.
• The site area used for charging is wrong or includes land you do not occupy.
• A multi-unit site has charges split incorrectly between tenants.

Thinking about future changes

If you are planning building work, a car park extension or new drainage, think about the effect on surface water charges. Sustainable drainage features, such as permeable paving or attenuation tanks, may reduce how much rainwater reaches the sewer. Some wholesalers have indicated they may offer discounts where drainage is improved in this way. Keep records of any changes so that your charges can be updated.

Multi-site businesses

If you operate several premises, each may have different drainage arrangements and may be served by a different wholesaler with its own charging method. A single portfolio-wide review can be more efficient than checking site by site. Our multi-site water bill review is designed for this.

Related charges

Surface water drainage is one part of the wastewater element of your bill. To understand the rest – foul sewerage, highway drainage and trade effluent – read our guide to understanding wastewater charges.

Get your drainage charges reviewed

Our surface water drainage charge review checks whether these charges appear to match your site. You can upload your bills to get started. Any rebate depends on your wholesaler's decision, and we will explain any fees before any work goes ahead.

Frequently asked questions

Updated 4 October 2026. This guide is general information, not legal or financial advice. Charges and rules vary by water company and nation.