Commercial Wash Bay Design: Equipment, Water, Containment, and Workflow

A wash bay is a system, not a room with a pressure washer in it. The machine, the water supply, the containment, the drainage, and the workflow all constrain each other — and the cheapest time to get them consistent is before anything is poured.

We supply and service the equipment for commercial wash bays across Northeast and North Central Florida, and we’d rather be involved while the plan is still on paper. This is the sequence we walk facilities through, and the questions that decide the answer.

Step 1: What Has to Be Washed, and How Often

Start with throughput, not equipment. How many vehicles or units per shift? How big, how dirty, and how much of the soil is grease or oil rather than road film?

Two numbers fall out of this immediately: the flow you need (GPM covers ground faster) and whether you need heat (grease and oil mean hot water; general exteriors often don’t). Our sizing guide does the arithmetic, and the buying guide covers drive power and heat source.

Step 2: Water Supply

This is where more projects fail than anywhere else. A pressure washer cannot deliver more flow than it’s fed.

• Confirm available flow and pressure before specifying a machine. A 4 GPM machine needs at least 4 GPM of supply, at adequate inlet pressure.
• Check line size. An undersized supply line starves the machine no matter what the source can deliver.
• Consider storage. A break tank with a transfer pump decouples the machine from a marginal supply and lets you use a smaller line than the machine’s rating would otherwise demand.
• Plan refill, not just draw. If you’re adding an onboard or break tank, size it to a duty cycle rather than a guess — capacity ÷ flow rate is the runtime, and a 200-gallon tank feeding 4 GPM is about 50 minutes.

Step 3: Containment, Drainage, and Discharge

Wash water carries oil, grease, suspended solids, heavy metals, and detergents. It is not rainwater, and it cannot go to a storm drain. Florida DEP’s BMP guidance for vehicle and equipment washing is specific about the options:

• Discharge to a sanitary sewer — generally preferred, requires prior approval from the wastewater utility, possibly with pretreatment
• Contain and haul to a permitted treatment, storage and disposal facility
• Discharge to land only when treated to prevent groundwater pollution

Design consequences that belong in the plan from the start:

• Wash on an impermeable surface with containment sized to the volume you generate — a 4 GPM machine produces 240 gallons an hour
• An oil/water separator ahead of discharge, plus solids and grit capture
• Slope and a trench drain sized for peak flow, not average
• Keep the wash area away from repair bays, fuel points, and chemical storage so runoff can’t carry anything from them
• Consider closed-loop reclaim once volume makes water handling a real cost — it also reduces what you discharge
• High-pressure, low-volume equipment reduces the volume you have to handle for the same cleaning result, which is a design decision made at the machine, not the drain

Step 4: Power and Ventilation

The drive type follows from the site:

• Electric drive where you have the service and want no exhaust indoors — confirm voltage, phase, and amperage at the bay, not at the panel room. Higher-output industrial electric units often need 230V single-phase or three-phase.
• Engine drive for independence and mobility, with ventilation and carbon monoxide designed in. Engine exhaust indoors is not a detail to solve later.
• Burner ventilation on hot water machines, including LP and natural gas installations, which also need the gas supply and burner sizing planned.
• Lighting and electrical placement consistent with a wet environment.

Step 5: Layout and Workflow

The equipment spec and the bay geometry should be decided together:

• One bay or drive-through? Drive-through raises throughput and cost.
• Gun count. Two operators with two guns needs the pump, burner, and water supply sized for combined flow — it’s not a plumbing change.
• Hose management. Booms or overhead reels keep hoses off the floor, which is both a safety and an equipment-life decision.
• Drying and finishing space — a bay with nowhere to dry vehicles has a workflow problem, not a drying problem.
• Chemical storage and injection located so drums can be handled safely and lines can be serviced.
• Access for service. Leave room for a technician to reach the burner, pump, and coil. The machine boxed into a corner is the machine that gets neglected.

Step 6: Specify the Equipment to the Bay

Once the bay is defined, the machine spec is largely determined: flow from throughput and gun count, pressure from soil, heat from soil chemistry, drive from power availability, and configuration from whether the equipment needs to move.

That’s the point where we can quote with confidence rather than guessing — and where the sizing guide and trailer systems page come in.

Who Does What

We supply and service the cleaning equipment and chemistry, and we’ll advise on water, containment, and ventilation requirements as they relate to it. The bay itself — civil work, drainage, electrical, gas, and permitting — is your contractor’s and your utility’s territory, and the discharge approval is a conversation with your wastewater utility and DEP district office.

What we can do is make sure the equipment you buy doesn’t fight the bay you built, and that the plan accounts for wash water before you’re retrofitting a separator into finished concrete.

Frequently Asked Questions

How much space does a commercial wash bay need?
Enough to work around the largest vehicle plus hose management and safe access to the equipment. Practical minimums depend on the vehicle class — a tandem-axle truck needs considerably more maneuvering room than a pickup — and on whether you’re washing one or two vehicles at once.

Do I need an oil/water separator?
If you’re discharging wash water to a sanitary sewer, pretreatment requirements come from your wastewater utility, and an oil/water separator is commonly part of that. Build it into the plan rather than adding it afterward.

Can I wash in a parking lot instead of a bay?
Yes, but the wash water still has to be managed — that’s true of mobile washing as much as fixed bays. DEP’s guidance expects containment to a sewer with approval, or containment and haul-off.

What size machine for a two-bay operation?
That depends on throughput per bay and how many operators you’ll run, not on the bay count. Tell us units per shift per bay and we’ll size it — two bays with one operator each may need less machine than one bay with three.

Can you provide equipment documentation for a project?
Yes — formal quotes, W-9, certificates of insurance, equipment specifications, manufacturer literature, and SDS and technical data for chemistry on request.

Plan the Bay With Us

Send us what you’re washing, how many units per shift, the space you have, and where the water is going. We’ll spec the equipment side and flag the constraints before they become change orders.

The one-page planning worksheet below is the same set of questions we start from — free, no form required.

Download: Commercial Wash Bay Planning Worksheet (PDF)

Call (904) 693-2155 or request a quote. Sun Pro Supply is the exclusive authorized Hotsy dealer for Duval, Clay, St. Johns, Putnam, Marion, Alachua, and Columbia counties, and an authorized retail and repair center for Ramteq and other major commercial brands. See also fleet and truck wash equipment, our chemistry selection guide, and service and maintenance.