A 50 gallon water tank for pressure washer rigs hits a sweet spot that few other sizes match. It is small enough to mount on a compact trailer or in the bed of a pickup, yet large enough to carry a real working supply of water for mobile cleaning where no spigot exists. Ask ten operators what they run and a surprising number will point to a 50 gallon tank as the backbone of a startup rig or a secondary buffer on a bigger machine.
The problem is that the 50 gallon figure alone tells you almost nothing. Fifty gallons means different things depending on whether the tank is feeding a 2 GPM electric machine or acting as a buffer for a 5 GPM gas monster. It means different things whether you are filling from a customer’s spigot or hauling every drop you will use. And it means different things depending on the tank’s shape, outlet size, and how you plumb it.
This guide breaks down what a 50 gallon tank actually delivers, how long it lasts at common flow rates, how to size it to your machine, which styles exist, how to mount and plumb it safely, your refill options, and how to keep it working through every season. By the end you will know whether a 50 gallon tank is the right call for your pressure washing work.
What a 50 Gallon Water Tank Does on a Rig
A water tank on a pressure washer rig does one of two jobs, and sometimes both at once.
- Supply. When there is no water source at the job, the tank is the entire water supply. Every gallon the machine uses comes out of the tank, and you must refill or finish.
- Buffer. When there is a water source, the tank smooths the flow between the spigot and the pump, storing water so the pump never starves even when supply pressure or flow is marginal.
Most mobile setups use the tank as supply. Most rigs working at residential jobs use it as a buffer, filling from the customer’s spigot and letting the tank absorb the difference between what the house can deliver and what the machine demands. A 50 gallon tank works well for both, which is why it is such a common choice.
The magic of a buffer tank is that it breaks the direct link between supply and pump. If a house spigot can only push 3 GPM but your machine pulls 4 GPM, a bare connection starves the pump and causes cavitation. Add a 50 gallon buffer and the tank drains slowly during heavy use and refills during pauses, feeding the pump steadily and protecting it from the spikes that ruin pumps. Our look at making your rig self-sufficient with a water tank covers this buffer logic in more detail.
How Long Does 50 Gallons Last?
The runtime question is the one every new operator asks. Fifty gallons lasts exactly as long as your machine’s flow rate allows, and flow is measured in GPM, gallons per minute. Divide 50 by your GPM and you get the theoretical minutes of continuous spray.
| Machine Flow (GPM) | Runtime on 50 Gallons | Typical Machine Class |
|---|---|---|
| 1.5 GPM | ~33 minutes | Small electric |
| 2.0 GPM | ~25 minutes | Full-size electric |
| 3.0 GPM | ~17 minutes | Small gas |
| 4.0 GPM | ~12.5 minutes | Mid-size gas |
| 5.0 GPM | ~10 minutes | Large gas |
Those numbers assume continuous spraying, which never happens in real work. You pause to move, to change nozzles, to apply soap, to inspect, and every pause stretches the runtime. Real-world jobs often get 30 to 50 percent more working time than the raw division suggests because the trigger is released so often. Still, the table is the honest starting point: on a 4 GPM machine, a 50 gallon tank is roughly 12 minutes of nonstop water, so a full vehicle wash with no refill is unrealistic on tank supply alone.
This is why the 50 gallon tank mostly serves one of two roles. As a buffer, ten or fifteen minutes of draw is plenty because the tank refills constantly. As a standalone supply, fifty gallons is best for short, controlled jobs like rinsing a few pieces of equipment, a quick patio, or a spot-cleaning call where you top off between tasks. If you plan to run tank-only for a full driveway and house wash on a gas machine, step up to a larger tank, which is exactly the trade-off covered in our guide to a 100 gallon water tank for pressure washer rigs.
Sizing a 50 Gallon Tank to Your Machine
Sizing comes down to deciding what you want the tank to be: a buffer or a supply.
As a buffer
For buffering, the tank needs to hold enough water to cover the gap between supply flow and machine demand during the heaviest stretch of work. A practical rule is to keep a buffer reserve of at least ten times your machine’s GPM, and more if your supply is weak. A 4 GPM machine buffered by a 50 gallon tank holds more than enough reserve; you rarely need the whole 50 gallons to smooth the flow. Even a 20 or 30 gallon tank often buffers a 4 GPM machine fine. The 50 gallon size simply gives you extra margin and doubles as partial supply.
As a supply
For supply, work backward from the job. Estimate how many minutes of continuous spraying a typical job needs, multiply by your GPM, then add margin for refills. If a job needs about 20 minutes of spray on a 3 GPM machine, that is roughly 60 gallons, so a 50 gallon tank means at least one mid-job refill. If your jobs are shorter or your machine is smaller, 50 gallons covers many of them.
The honest summary: a 50 gallon tank is an excellent buffer for almost any gas machine and a workable supply tank for smaller machines or short jobs. It becomes limiting when you try to run long jobs on tank supply alone with a high-GPM machine.
Popular 50 Gallon Tank Styles and Specs
Not all 50 gallon tanks are shaped alike, and shape affects mounting, footprint, and how well they fit a rig.
| Style | Footprint | Best Use |
|---|---|---|
| Flat-bottom utility | Wide, low profile | Trailer decks, truck beds |
| Upright vertical | Small, tall | Tight corners, upright mounting |
| Narrow / slim | Thin, tall | Alongside equipment on a trailer |
| Conical bottom | Funnel base | Full drainage, low outlet |
A typical flat-bottom 50 gallon polyethylene utility tank measures roughly 38 inches long by 19 inches wide by 23 inches high and weighs about 27 pounds empty. It usually comes with a large threaded lid for filling and cleaning, a bulkhead outlet, and gallon indicators molded into the side. Many are made from FDA-approved resin, so they are safe for potable water, and they include UV inhibitors to resist sun damage. Match the outlet size to your plumbing; a 1 inch or larger outlet feeds a pump far better than a small one.
Poly tanks dominate because they are light, affordable, corrosion-proof, and easy to drill for fittings. Stainless and aluminum tanks exist for specialty rigs but cost far more and are heavier. For most operators, a quality polyethylene 50 gallon tank is the practical answer. Choosing the right tank overall is the subject of our pressure washing tanks guide to size and type.
Mounting a 50 Gallon Tank Safely
A 50 gallon tank is light when empty and heavy when full, and that weight is what breaks mounts, bends decks, and creates a hazard on the road. Water weighs about 8.34 pounds per gallon, so 50 gallons is roughly 417 pounds, plus the tank and fittings. The whole assembly approaches 450 pounds, and it sloshes.
| Contents | Approx. Weight |
|---|---|
| Empty 50 gallon poly tank | ~27 lb |
| Water (50 gal × 8.34) | ~417 lb |
| Fittings, hose, straps | ~5–10 lb |
| Total full | ~450 lb |
Mount the tank on a flat, structurally sound surface and secure it with straps or bands rated well above the full weight. Do not rely on a single strap. The tank should not be able to slide, tip, or lift, because a 450-pound shifting load on a trailer is dangerous at highway speed. Use a full-frame or deck that distributes the load, and reinforce thin sheet-metal floors with plywood or a steel plate so the tank does not dent the deck or punch through.
Keep the tank’s center of gravity low and centered over the axles when possible. On a trailer, a tall upright tank mounted high makes the rig top-heavy and unstable. On a truck bed, distribute the tank so it does not overhang or sit behind the rear axle where it acts like a lever. Our article on building a self-contained supply from a water tank walks through mounting and layout.
Plumbing a 50 Gallon Tank to the Pump
Getting water out of the tank and into the pump is where a lot of DIY rigs go wrong. The goal is unobstructed, air-free flow at a rate that meets or exceeds the machine’s GPM.
- Outlet size. Use at least a 1 inch bulkhead fitting. Anything smaller restricts flow and starves a gas machine.
- Keep it low. Mount the outlet near the bottom, but leave a small gap above the floor so sediment settles and does not enter the pump.
- Anti-vortex fitting. An anti-vortex or elbow fitting at the outlet prevents a swirling funnel that sucks air as the tank nears empty.
- Large feed hose. Run a short, large-diameter, crush-proof feed hose from the tank to the pump inlet. Long or thin feed lines cause pressure loss and cavitation.
- Strainer. A coarse inlet strainer keeps debris out of the pump without choking flow.
- Vent. Keep the tank lid vented so air can enter as water leaves, otherwise the tank develops a vacuum and flow stops.
If the tank sits below the pump inlet, gravity alone may not feed a high-flow machine. Many rigs add a small transfer or boost pump between the tank and the main pump to push water uphill. On flat or low-mounted tanks with a large, short feed line, gravity often works, but high-GPM machines frequently need the assist.
Refilling in the Field
If your 50 gallon tank is a supply, refilling strategy matters as much as the tank itself.
- Gravity fill from a spigot. The simplest method. Run a garden hose from the customer’s spigot to the tank lid and fill while you work. With a buffer setup, this often keeps up.
- Float valve. A float valve in the tank automatically shuts off when full, so you can leave a hose running without babysitting it.
- Transfer pump. For fast fills from a bulk source or another tank, a transfer pump moves water quickly.
- Bulk source. Some operators fill from a home-based bulk tank or a hydrant permit, hauling water to the job and refilling between stops.
- Scheduled refills. On tank-only jobs, plan refill points into the route so you never run dry mid-task.
Ask permission before using a customer’s water, and use a backflow preventer so you never contaminate their supply. A float valve plus a length of garden hose turns most residential jobs into a steady, hands-off fill, which is the best of both worlds: the tank buffers while the spigot replenishes.
Filling, Maintenance, and Freeze Care
A poly water tank is simple, but a little care keeps it clean and working.
- Rinse before first use to remove manufacturing residue.
- Keep it covered with its lid so debris, insects, and algae stay out.
- Clean periodically with a mild rinse; avoid harsh chemicals that degrade the resin.
- Check fittings for leaks and tighten bulkheads seasonally.
- Inspect straps and mounts for wear, especially after rough towing.
- Drain before freezing weather and store the tank dry if it will sit unused in winter.
Freeze damage is a common killer. Water expands as it freezes and can crack a poly tank, split fittings, or burst hoses. In cold climates, drain the tank completely at the end of the season, blow out the lines, and store it out of the weather. If you use the tank year-round in freezing conditions, insulate it and keep water moving, or drain it after each use. A cracked tank is a total loss, and the fix is entirely preventable.
Buying New or Used
New 50 gallon poly utility tanks are affordable and come with known history, which matters for potable water. Used tanks often sell cheap at farm supply resales and online marketplaces, but inspect carefully.
- Check for cracks around the outlet, lid, and any prior holes.
- Confirm the outlet size matches your plumbing needs.
- Smell the inside if the tank will hold drinking water; avoid tanks that held chemicals.
- Verify the resin rating for potable use if that is your intent.
- Test-fit fittings and make sure threads and bulkheads are sound.
Used tanks that held fertilizer, herbicide, or unknown liquids should never be repurposed for potable water, no matter how well they are rinsed; the resin can absorb chemicals. For cleaning water it is far less critical, but a tank that held a hazardous liquid should still be avoided. When in doubt, buy new, because a clean, unknown-history tank is worth the modest price premium.
Tank Accessories Worth Adding
A bare tank works, but a few inexpensive accessories turn it into a dependable part of the rig.
- Bulkhead fitting kit. A properly sealed bulkhead gives you a leak-free outlet that you can service without cutting the tank again.
- Ball valve. A valve at the outlet lets you shut off the water for pump maintenance and hose changes without draining the whole tank.
- Anti-vortex fitting. Keeps the pump from sucking air when the tank is low, which is one of the most common causes of pump cavitation.
- Vented lid. Allows air in as water leaves, preventing the vacuum that stops flow.
- Float valve. Automates refilling and prevents overflow when filling from a spigot.
- Strap or band kit. Purpose-made bands distribute the load and hold the tank far more securely than generic straps.
- Level gauge or sight tube. Lets you see how much water remains at a glance instead of guessing.
- Transfer or boost pump. Pushes water to the machine when the tank sits low or the run is long.
None of these items is expensive, and together they remove the small frustrations that turn a simple tank into a constant headache. The anti-vortex fitting and vented lid in particular address the two most common flow problems, air in the line and vacuum lock, so prioritize those if you are building on a budget. Our overview of self-sufficient water tank setups ties these accessories into a complete rig.
Water Quality and Filtration
Where your water comes from affects both the job and the machine. A 50 gallon tank holding well water, hauled water, or recycled water can carry grit, minerals, and debris that wear pumps and leave spots.
- Sediment strainer. A coarse strainer at the tank outlet traps sand and grit before they reach the pump.
- Filter washer at the inlet. A screen washer on the pump inlet catches smaller debris and is easy to clean.
- Soft water where possible. Hard water leaves mineral spots on glass and painted surfaces; a soft water source produces a cleaner rinse.
- Spot-free rinse. For vehicle work, a final rinse with filtered or deionized water prevents water spots entirely.
- Clean the tank. Rinse the tank periodically so sediment does not build up and get stirred into the supply.
Water quality also affects what you can carry. A tank that held potable water can be used for cleaning and, if kept clean, for drinking, while a tank used for cleaning should never be treated as potable. Keep the two purposes separate and label your tanks if you use them for both. On paid jobs, clean water is part of the result, and gritty or hard water undercuts the work you just did.
Frequently Asked Questions
How long does a 50 gallon water tank last on a pressure washer?
Divide 50 by your machine’s GPM. A 2 GPM machine gets about 25 minutes of continuous spray, a 4 GPM machine about 12.5 minutes. Real jobs last longer because you pause, but plan for refills on tank-only work.
Is 50 gallons enough for a pressure washing business?
It works well as a buffer for most gas machines and as a supply tank for smaller machines or short jobs. For long jobs on high-GPM machines, a larger tank or a refill plan is better.
Can a 50 gallon tank run a pressure washer without a water source?
Yes. Use it as a standalone supply and refill as needed. High-GPM machines drain it quickly, so add a transfer pump or schedule refills for longer jobs.
How much does a full 50 gallon tank weigh?
Water is about 8.34 pounds per gallon, so 50 gallons weighs roughly 417 pounds, plus about 27 pounds for the tank and a few pounds of fittings, for a total near 450 pounds.
Do I need a buffer tank if I have a water spigot?
Often yes. A buffer tank protects the pump when supply flow or pressure is marginal, storing water during heavy use and refilling during pauses. It prevents the cavitation that shortens pump life.
What size feed line should I use from a 50 gallon tank?
Use at least a 1 inch outlet and a short, large, crush-proof feed hose to the pump inlet. Smaller or longer lines restrict flow and starve high-GPM machines.
Final Thought
A 50 gallon water tank for a pressure washer rig is a Goldilocks size: light enough to mount on compact rigs, heavy enough to matter when full, and flexible enough to serve as either a buffer or a supply. Its value comes down to matching it to the job. As a buffer, it protects pumps and smooths marginal supply on nearly any machine. As a supply, it covers smaller machines and shorter jobs, with refills for the rest.
Get the sizing right, mount it so 450 pounds of sloshing water never becomes a hazard, plumb it with a large feed line and a vented lid, and protect it from frost. Do those things and a modest 50 gallon tank becomes one of the most reliable parts of your setup, quietly feeding the machine while you focus on the work instead of the water.