Quick answer: Setting up a fleet wash bay requires more than installing a pressure washer and a drain. Wash water from vehicle cleaning is trade effluent and cannot be discharged to surface water drains without an Environment Agency permit. Discharge to foul sewer requires trade effluent consent from your sewerage undertaker. The wash bay itself needs a contained wash pad, an interceptor for hydrocarbon separation, and a connection to the appropriate drainage. Equipment specification depends on fleet type -- hot water is the standard for HGV and PSV fleets. This guide covers everything from the drainage design to the permit application to the pressure washer specification.
A fleet wash bay is a significant infrastructure investment that, done correctly, reduces vehicle maintenance costs, improves fleet presentation, supports MOT and inspection readiness, and demonstrates environmental compliance to clients and auditors. Done incorrectly, it creates an ongoing environmental liability and potential criminal exposure under the Water Resources Act 1991.
Step 1 -- Drainage design
The drainage design is the foundation of a compliant wash bay. Three things must be in place:
A contained wash pad. The wash area must be impermeable -- concrete with sealed joints, or resin-bound surface -- so that wash water cannot run off the pad into permeable ground. The pad must drain to a collection point, not to a surface water drain.
A petrol/oil interceptor. Wash water from vehicle cleaning contains hydrocarbons -- fuel residue, oil, grease. An interceptor (also called an oil interceptor or separator) removes free-floating hydrocarbons before the water passes to the drain. This is a requirement under the Environmental Permitting Regulations for any site where vehicle washing generates hydrocarbon-contaminated water.
Connection to foul sewer, not surface water. After passing through the interceptor, wash water must go to foul sewer -- not to a surface water drain, not to a soakaway, not to a ditch or watercourse. Surface water drains flow directly to the environment untreated. Even with an interceptor, wash water containing detergents and dissolved contaminants cannot legally go to surface water without an EA permit. See: Environmental Permitting guidance
Step 2 -- Trade effluent consent
Before you can discharge wash water to the foul sewer, you need trade effluent consent from your sewerage undertaker -- Severn Trent, Thames Water, Yorkshire Water, Anglian Water or similar depending on your location.
Applying for trade effluent consent involves:
- Completing an application form with your sewerage undertaker
- Describing the nature and volume of the trade effluent (vehicle wash water -- what chemicals used, maximum daily volume)
- Providing drainage plans showing the interceptor and connection to foul sewer
- Agreeing to any conditions the undertaker sets (pH limits, temperature limits, monitoring requirements)
Trade effluent consent is a formal legal consent. Operating a vehicle wash without it and discharging to foul sewer is an offence under the Water Industry Act 1991. Sewerage undertakers do inspect and enforce, particularly where complaints are received about blocked sewers or treatment plant issues.
Step 3 -- Equipment specification
The correct pressure washer specification for a fleet wash bay depends on the fleet type:
HGV and PSV fleet washing
Hot water pressure washing is the standard for HGV, bus, coach and large van fleets. Hot water at 70-90 degrees C removes road film, diesel soot, grease and brake dust more effectively than cold water -- reducing chemical use and cleaning time. For HGV washing, high flow rate matters as much as maximum pressure -- 15-20 LPM at 150-200 bar is the typical fleet wash specification. Cold water machines at maximum pressure but low flow rate are slower and less effective on large vehicle surfaces.
Van and light fleet washing
Cold water electric machines are adequate for light van fleet washing where vehicles do not accumulate heavy diesel soot or road film. 110-140 bar, 8-12 LPM is the typical light fleet specification.
Plant and construction equipment
Plant washing -- excavators, dumpers, telehandlers -- requires high flow rate for mud and clay removal. A surface cleaner attachment is effective for flat surfaces on plant equipment. For sites where plant washing generates heavily contaminated water (clay-laden, potentially with fuel contamination), the drainage and interceptor specification needs to reflect the higher contamination load.
View hot water pressure washers | View electric pressure washers | Fleet and logistics hub
Step 4 -- Chemical selection and COSHH
Fleet wash chemicals -- traffic film removers (TFRs), degreasers, wheel cleaners -- require COSHH assessment. From August 2026, updated GB CLP classifications apply to a range of cleaning chemicals. Check that your chemical supplier has updated their Safety Data Sheets before the August 2026 deadline. See: Chemical reclassification August 2026
Related guidance
Environmental Permitting and trade effluent | Fleet and logistics hub | Clean Air Zones and DVS | Environmental Permitting article
