Nobody starts a cleaning business worrying about drainage.
You buy a good machine, you get good at the work, and the water goes wherever the ground slopes. It has always gone there. Nobody has ever said anything.
Then one job goes wrong. A car park with a gully that runs straight into a brook, a bit of traffic film remover, a member of the public who notices the colour of the water, and a phone call from the Environment Agency.
This is the least discussed part of commercial pressure washing and the one most likely to produce a genuinely serious bill.
Two drains, and the difference is everything
Almost every commercial site has two drainage systems, and most people cannot tell them apart.
Foul drains carry water from toilets, sinks and kitchens to a sewage treatment works, where it is treated before discharge. Getting something into the foul system is manageable, and often permitted with the right consent.
Surface water drains carry rainwater from roofs, car parks and yards. In most cases they discharge, untreated, straight into a stream, river or soakaway. Nothing between the gully and the watercourse.
The default assumption should be that a yard or car park gully is surface water. Roof downpipes and car park drains almost always are.
So the rule that matters: anything other than clean rainwater entering a surface water drain is a pollution offence. Not a technicality, not a warning. Water companies and the environmental regulator both prosecute for it.
Why your run-off is not clean water
It feels like water. It is not, once it has been on a surface.
Vehicle washing produces run-off carrying oil, diesel, brake dust with heavy metals in it, traffic film remover, and the detergents you applied deliberately.
Building and paving cleaning produces run-off with algaecides, biocides, silt and whatever was growing there.
Workshop and plant cleaning produces oil, grease, coolant and hydraulic fluid.
Even without chemicals, silt alone is a pollutant. It smothers riverbed habitat. "I only used water" is not the defence people expect it to be.
And detergents described as biodegradable are still harmful in a watercourse. Biodegradable describes what happens eventually, not what happens to fish this afternoon.
What compliant looks like
On a fixed site
A designated wash bay that drains to an interceptor, sometimes called an oil separator. The interceptor holds back oil and silt so what continues on is far cleaner.
Two things people get wrong about interceptors. They need servicing on a schedule, and an unserviced one stops working and passes oil straight through. And they do not remove detergents, so what leaves still needs an appropriate destination.
A trade effluent consent from your water company where you discharge to foul. This is a formal agreement stating what you may discharge, in what volume and at what strength. It is not difficult to obtain and it is what makes the discharge lawful.
Bunding or a fall that keeps wash water inside the bay and out of the yard drainage.
For mobile work
This is harder, and it is where most businesses are exposed.
Ask before you start where the water goes. On any commercial site, the facilities or site manager should know. If nobody knows, treat every gully as surface water.
Use drain mats or covers over nearby gullies while you work. Inexpensive, portable and the single most effective control available to a mobile operator.
Recover the water where you can. Wet vacuum recovery systems and portable bunded wash mats collect run-off for proper disposal. On sensitive sites they are increasingly a condition of being allowed on at all.
Consider waterless or low-water methods for light valeting. No run-off, no problem.
Never work directly over a gully. Reposition the vehicle rather than the drain.
The commercial argument, not just the legal one
Two reasons this is worth sorting out beyond avoiding prosecution.
It wins contracts. Facilities managers, main dealers, fleet operators and local authorities increasingly ask about run-off and effluent consent during procurement. Having a straight answer separates you from competitors who go quiet.
It protects you from the client's failings. If you pollute using a client's drainage, being able to show you asked, you covered the gullies and you recovered the water is what shifts the position.
Put it in writing. A short method statement covering water management, attached to your quote, is a genuine differentiator on commercial work.
If something has gone into a drain
Stop. Do not keep working and do not hose it through.
Contain it if you safely can. Drain mats, absorbents, anything that stops more entering.
Report it. The Environment Agency incident hotline is 0800 80 70 60, 24 hours. Equivalent bodies cover Scotland, Wales and Northern Ireland. Notify the water company too if it entered the foul system.
Self-reporting matters enormously. An operator who rings within the hour is treated very differently from one whose pollution is reported by a member of the public two days later.
Frequently asked questions
Can pressure washing waste water go down the drain?
Not into a surface water drain, which usually discharges untreated straight to a watercourse. Run-off from vehicle, building or plant cleaning carries oil, silt, metals and detergents and putting it there is a pollution offence. Discharge to a foul drain may be permitted, but it normally requires a trade effluent consent from your water company.
Do I need a licence to run a mobile valeting business?
There is no single licence, but you must not cause pollution, which in practice means managing run-off. On fixed sites you are likely to need a trade effluent consent to discharge to foul. For mobile work, cover nearby gullies, ask the site where its drains go, and use water recovery on sensitive sites.
What does an interceptor do?
An interceptor, or oil separator, holds back oil and silt from wash water so cleaner water continues onward. It must be serviced on a schedule, because an unserviced interceptor stops retaining oil and passes it straight to the drain. Interceptors do not remove detergents, so the destination still matters.
Is biodegradable detergent safe to wash into a drain?
No. Biodegradable describes what eventually happens to the chemical, not its immediate effect on a watercourse, where it can still harm fish and invertebrates. Biodegradable products are better than the alternatives but they do not make discharge to a surface water drain lawful.
How do I know if a drain is foul or surface water?
Assume yard, car park and roof drains are surface water unless you have been told otherwise, and ask the site manager on commercial jobs. On sites you control, get a drainage plan and physically mark every gully, using different colours for foul and surface water, so nobody has to guess in a hurry.
The bottom line
The machine is the easy part. Knowing where the water goes is what separates a business that scales onto commercial contracts from one that gets a phone call it cannot afford.
Ask the question on every site, carry drain mats, and put your water management in writing on the quote.
Kränzle UK supplies professional machines to mobile operators and fixed wash bays across the UK, along with the accessories that make water management practical. Talk to us about how you work, not just what you want to buy.