Vehicle washing regulations UK: where can wash water go at your depot?

In England, vehicle wash water counts as contaminated, so it must not go into a surface water drain. It can go to the foul sewer if your water company gives permission. Otherwise it goes into a sealed system, for reuse, treatment on site or removal by a registered waste carrier. Scotland, Wales and Northern Ireland follow similar rules.

Most depots inherit the drains they were built with, and few of those drains were laid with a wash bay in mind. Plenty of the sites we work on have no wash bay and no drain the wash water can legally go into. So before any wash starts, our team checks the nearby drains, the site drainage and how the water will be contained and removed. This guide sets out the rules behind those checks: where wash water can go, why an oil interceptor isn't the answer people hope it is, what planning conditions say, and who is responsible when a contractor does the washing.

Updated 26 October 2026. Rules checked on GOV.UK, legislation.gov.uk and NetRegs the same day. This is a plain-English guide, not legal advice.

Why does vehicle wash water count as contaminated?

Because of what comes off the vehicle. A lorry or refuse vehicle sheds road film, mud, oil, grease, diesel and brake dust into the wash water, and an RCV adds waste residue on top. Then there's the traffic film remover or detergent used to shift it all. GOV.UK's Pollution prevention for businesses guidance lists "vehicle washing, wheelie bin washing or yard cleaning" among the activities that produce contaminated water, and says plainly: "you must make sure it does not cause pollution."

The drain it runs into decides whether it does. GOV.UK puts it in one line: "Surface water drains discharge directly to the environment." A yard gully on the surface water system can lead to a stream or a soakaway, with no treatment on the way. Foul drains go to a sewage works.

You can usually tell which is which from the manhole covers, if they've been marked the way GOV.UK recommends:

If the covers aren't marked, or nobody's sure, GOV.UK says you may need a full drainage survey.

Getting it wrong is expensive. GOV.UK says that if you pollute, "you could get an unlimited fine, go to prison for up to 5 years, or both", and you may also have to pay for the whole clean-up.

Where can vehicle wash water legally go?

In England, GOV.UK gives two ways to deal with contaminated water: the foul drain with permission, or a sealed system. Split the sealed system into its two endings and you get three routes a depot can actually use:

The permission in route 1 isn't a formality. Under section 118 of the Water Industry Act 1991, trade premises in England can discharge trade effluent into a public sewer only with the sewerage undertaker's consent. Discharging without it is an offence, punishable by a fine. A combined drain needs the same permission: GOV.UK says it can take both kinds of water, but "you'll still need permission from your water company to use it for contaminated water."

Route 3 comes with duty of care paperwork. GOV.UK's guide to managing your waste says to check your waste carrier is registered and to "complete a waste transfer note for each load of waste that leaves your premises."

What isn't on the list: the surface water drain, a soakaway, or letting the water run across the yard until it finds a gully.

When we wash vehicles on a site with no suitable drain, we use route 3. The water is captured, recovered and taken away for disposal, and we hold waste carrier licences for England and Scotland.

Do you need an oil interceptor for vehicle washing?

An oil interceptor, also called an oil separator, holds water long enough for oil to float off before the water flows on. GOV.UK says you may need one where there's a risk of oil getting into the drains: car parks over 800m² or with 50 or more spaces, vehicle maintenance areas, roads and refuelling areas. Plenty of depots tick at least one of those boxes.

Here's the catch. An interceptor doesn't make wash water safe to put down a surface water drain. GOV.UK says separators "do not work if they are incorrectly sized, not maintained or there's detergent in the water". Detergent breaks the oil up so it travels through with the water instead of floating. Scotland, Wales and Northern Ireland's GPP 13 guidance goes further and says wash bay run-off "must not be discharged through the oil separator".

So washing a lorry over the yard gully because "it goes through the interceptor" doesn't fix anything. An interceptor in front of a consented foul sewer connection is a different matter. That's common on wash bays, as the planning condition in the next section shows.

If you have an interceptor, GOV.UK and the British Standard it refers to expect:

• a check at least every 6 months for oil and silt build-up, and to see that every part is working
• emptying when oil or silt has built up, after a spill, or when the alarm goes off
• a high-level alarm, which has been a legal requirement for separators supplied in England, Wales and Scotland since 1 January 2021
• an integrity test at least every 5 years, with service and maintenance records you can show an inspector
• emptying by a company with a waste carriers licence. The trapped oil and sediment is hazardous waste and needs a hazardous waste consignment note

What planning conditions say about wash bays

If you're building a wash bay, or a new site comes with one, check the planning conditions. Councils can spell out exactly where the water goes. Here's a real one from Doncaster Council's planning records:

"Any water run off from the vehicle wash down area shall be discharged to the public foul sewer"

The rest of the condition says the run-off must pass through a suitable oil, petrol and grit interceptor, and that the system must be working before the site is brought into use. The reason given is "to avoid pollution of the public sewer and land drainage system." The water company's consent sits on top of that, because the planning condition doesn't give you permission to use their sewer.

It's a useful benchmark if you're changing an existing yard. GPP 13, the guidance used in Scotland, Wales and Northern Ireland, adds design advice that's sensible anywhere:

• Put a roof over the wash area if you can, so rainwater doesn't add to the volume you have to treat.
• Keep the run-off in with channels, gullies, falls in the surface and kerbs.
• Send it through a silt trap or settlement tank first.
• Make the wash bay an impermeable area with no connection to the surface water drains.

A permanent wash bay can be costly to build and run, and on some sites it isn't practical at all. That's where the next option comes in.

No wash bay or drainage? How a wash mat set-up works

A site with no wash bay and no suitable drain can still have its vehicles washed, as long as the water never reaches the ground or a drain. That means a contained wash area that's put down for the job and taken away after it.

Peel Ports is the clearest example we have. More than 30 port tugs needed cleaning, and there was no wash area, no suitable drainage and no mains water. Ordinary pressure washing was ruled out because the contaminated wash water posed an environmental risk. So we brought hot-water pressure washers on our own water supply, built a portable wash mat on site to form a contained area, recovered the water, grease and oil as the tugs were washed, and took it all away for disposal. Then the mat came up and the site went back to normal use. That's route 3 from the table above, done on a dockside.

Our guide to why wastewater recovery is essential walks through the mat set-up step by step, so we won't repeat it here.

Two points matter if you're bringing in a contractor. GPP 13 says that when a contractor washes on your site, "it's your responsibility to provide appropriate facilities", and that landowners are responsible for pollution caused by contractors working there. In England, GOV.UK says you "must not let your business or organisation cause or allow pollution." Either way, the depot shares the risk. Before any mobile wash, ask:

• Where does the water go, and how is it contained?
• Who takes it away, and are they a registered waste carrier?
• Will you get a waste transfer note for each load?
• Do the RAMS cover the drains on your site?

In Scotland, Wales and Northern Ireland, GPP 13 also says jet washing and steam cleaning should take place in a designated wash bay, which it defines as an impermeable area with no connection to surface water drains. If you're there, agree how a temporary wash area will meet that before work starts. Our environmental and compliance cleaning team covers wastewater recovery and drain protection, and we're registered with SEPA in Scotland.

Vehicle wash water checklist for depots

Work through this once for each site, then again whenever the yard, the drains or the washing arrangements change.

If the honest answer to some of these is "not sure", it's fixable. Our guide to washing commercial vehicles without a wash bay covers the options when the drains rule out a fixed wash area.

Need vehicles washed on a site where the water can't go down the drain? Tell us about the site through our quote form or call 0800 6124 780. We reply within 2 business hours, and you can book a site survey to check the drainage before anything else is arranged.

Vehicle washing regulations: frequently asked questions

1. Can you wash a lorry over a surface water drain?

No. GOV.UK says only clean water should go into a surface water drain or soakaway, because surface water drains discharge straight to the environment. Vehicle wash water is contaminated, so it goes to the foul sewer with permission or into a sealed system.

2. Do I need permission to put vehicle wash water down the foul sewer?

Yes. You need consent from your water company, and that applies to combined drains too. Under section 118 of the Water Industry Act 1991, discharging trade effluent to a public sewer without consent is an offence.

3. Does an oil interceptor make vehicle wash water safe to discharge?

No. GOV.UK says separators don't work if there's detergent in the water, and GPP 13 says wash bay run-off must not go through the oil separator. An interceptor can still sit in front of a consented foul sewer connection, as some planning conditions require.

4. How often should an oil interceptor be emptied?

Check it at least every 6 months, and empty it when oil or silt has built up, after a spill, or when the alarm goes off. It must be emptied by a company with a waste carriers licence, and the waste is hazardous.

5. Is PPG 13 still in force?

No. In England, follow GOV.UK's pollution prevention for businesses guidance. In Scotland, Wales and Northern Ireland, GPP 13 (Vehicle washing and cleaning) covers the same ground. It's published by Natural Resources Wales, the Northern Ireland Environment Agency and SEPA, and says it isn't regulatory guidance in England.

6. What are the penalties for polluting with wash water?

GOV.UK says polluting can mean an unlimited fine, up to 5 years in prison, or both, plus the cost of the clean-up. Discharging trade effluent to a sewer without consent is a separate offence carrying a fine.

7. Who is responsible if a contractor washes vehicles on our site?

You share the responsibility. GPP 13 says the site owner must provide appropriate facilities and is responsible for pollution caused by contractors. In England, GOV.UK says a business must not cause or allow pollution. Ask any contractor where the water goes, in writing.

8. Can vehicles be washed on a site with no drainage at all?

Yes. The wash happens on a contained wash mat, and the water is recovered and taken away by a registered waste carrier. Our guide to how mobile fleet washing works at your depot shows what the team brings and what your site provides.

9. Can vehicle wash water be recycled?

Yes. GOV.UK lists a sealed system for reuse as one of the allowed routes, and GPP 13 calls recycling "the best environmental option". Recycling systems still collect silt and sludge, which has to be removed as waste.

10. What are the rules in Scotland, Wales and Northern Ireland?

The same principles apply: no wash water in surface water drains, consent for the sewer, and a registered carrier for anything taken away. Guidance comes from GPP 13 and NetRegs, not GOV.UK's England page. NetRegs also says new built-up areas in Scotland, such as yards, must drain run-off through sustainable drainage systems (SUDS).