Buffer Tank for Pressure Washer: When You Need One, How to Size It, and What to Buy

Most homeowners on municipal water with a standard 3/4-inch garden hose will never need a buffer tank. But if you are on well water, pulling from a rain barrel, or running a slow-flow spigot, this accessory can prevent the kind of pump damage that costs more than the tank itself. Here is how to figure out if you need one, how to size it right, and what to look for when buying.

What a Buffer Tank Actually Does for Your Pressure Washer

A buffer tank sits between your water source and the pressure washer inlet. Its job is simple: store enough water so the pump always has the flow rate it demands, even when the source cannot deliver that flow on demand.

Here is why that matters. Every electric pressure washer has a rated GPM — the gallons per minute the pump needs at the inlet to run correctly. A unit rated at 2,000 PSI and 1.8 GPM needs 1.8 gallons arriving every minute. If your well delivers 0.7 GPM through a 1/2-inch line, the pump is trying to pull more water than exists. The result: the pump draws air, the unloader valve cycles, the motor starts and stops, and internal components overheat.

A buffer tank solves this flow mismatch. It fills slowly from your low-flow source, then holds a reservoir of water that the pump can draw from at full GPM. The tank bridges the gap so the pump runs continuously instead of starving and cycling.

This is an accessory problem, not a machine quality problem. I have seen homeowners return perfectly good pressure washers because they assumed the machine was defective — when the real issue was a well that could not keep up. A $50 tank would have saved them the hassle. If you want to understand how accessories extend the life of your machine rather than replacing it, our electric pressure washer overview covers the full picture.

Signs Your Water Supply Is the Real Bottleneck

Before you buy a buffer tank for power washer use, diagnose the problem. A buffer tank only fixes one thing: insufficient inlet flow. If the root cause is something else, you will waste money and still have the same issue.

Here are the symptoms that point to a water-supply bottleneck:

• Pressure washer starts and stops repeatedly when you hold the trigger — this is the classic sign of the pump drawing air because inlet flow cannot match demand. For a full breakdown of cycling causes, see our guide on why your pressure washer starts and stops.
• You are on well water with a recovery rate below 2 GPM, or your supply line is 1/2-inch diameter instead of 3/4-inch.
• You are pulling from a rain barrel, creek, or gravity-fed system — these almost always need a buffer because gravity alone rarely delivers adequate GPM.
• Your spigot output is weak — if the garden hose barely fills a 5-gallon bucket in more than 3 minutes, your source is under 1.7 GPM, which is below what most residential washers need.

Run a bucket test before buying anything

Grab a 5-gallon bucket and a timer. Open your spigot fully into the bucket and time how long it takes to fill. Divide 5 by the minutes. That is your source GPM. Now compare it to your pressure washer’s rated GPM. If your source delivers less than the washer demands, you have found the problem. If the numbers are close or above, the bottleneck is elsewhere — check your hose for kinks, inspect the inlet filter, and look for air leaks at the connections.

Most homeowners on municipal water with a 3/4-inch hose and normal pressure (40–60 PSI at the spigot) will measure 5–8 GPM. That is more than enough for any residential electric pressure washer. If you are in that group and your washer is cycling, the problem is not water supply.

How to Size a Buffer Tank for Your Pressure Washer

Once you have confirmed the problem is low inlet flow, sizing the buffer tank comes down to a practical calculation. You are filling the gap between what your source delivers and what your washer needs, for the duration you want to run continuously.

Here is a straightforward way to estimate:

The formula: Tank gallons = (Pressure washer GPM − Source GPM) × Minutes of continuous use.

Example: Your washer is rated at 2.0 GPM. Your well delivers 0.8 GPM. You want to wash your driveway for 15 minutes without stopping. That is (2.0 − 0.8) × 15 = 18 gallons minimum. A 20-gallon tank gives you a small margin. A 35-gallon tank gives you room for longer sessions.

For most residential homeowners, a 20–35 gallon buffer tank is the practical range. If you are doing commercial work — washing storefronts, fleet vehicles, or large concrete areas — you may need 50–100+ gallons. But bigger is not always better. A 100-gallon tank for a 1.2 GPM gap is overkill. You are paying for capacity you will not use, and 100 gallons of water weighs about 830 pounds, which makes the tank hard to move and store. Match the tank to your actual gap and session length.

When you are ready to pair the right washer with the right water-supply setup, shop electric pressure washers for cars, decks, patios, driveways, and home cleaning to find a unit whose GPM matches your task.

What to Look for When Buying a Buffer Tank

Not all buffer tanks are equal, and the cheapest option is not always the right one — especially when the tank is protecting a pump that costs $80–$200 to replace.

• Material: Food-grade polyethylene is standard and perfectly fine for pressure washer use. You do not need stainless steel or aluminum. Polyethylene is UV-resistant, lightweight when empty, and does not corrode.
• Port size: Match your fittings. Most buffer tanks have 3/4-inch garden hose thread (GHT) inlet and outlet ports — the same as your spigot and washer inlet. If your fittings do not match, a $5 adapter solves it.
• Built-in filter or strainer: A screen at the inlet catches sediment, leaves, and debris before they reach the pump. This is not optional if you are drawing from a well or rain barrel. Sand and grit destroy pump seals and pistons.
• Portability: Water weighs about 8.3 lbs per gallon. A 35-gallon tank is roughly 290 lbs when full. Look for tanks with wheels, a low profile, or a flat bottom you can slide into a truck bed.
• Wall thickness: Thin-walled tanks flex and crack under the weight of water, especially in heat. Thicker walls cost a bit more but last multiple seasons.
• Price range: Expect $40–$80 for a 20–35 gallon tank and $80–$200 for 50–100 gallon tanks. Some users repurpose food-grade IBC totes (275 gallons) for high-volume setups. That works, but clean the tote thoroughly first — residue from whatever was stored in it can contaminate your washer’s pump.

A well-maintained buffer tank also feeds into your overall pressure washer lifespan. Keeping clean water flowing to the pump is one of the simplest ways to extend the machine’s service life. For a full rundown on maintenance and longevity, see our guide on how long your pressure washer lasts and how to protect it.

How to Connect a Buffer Tank to Your Pressure Washer

Setting up a buffer tank is straightforward. You do not need plumbing skills or special tools. Here is the process:

1. Position the tank. Place it above the pressure washer inlet — even 2 to 3 feet of elevation helps gravity push water to the pump. A tank sitting on a tailgate above a washer on the ground works fine.
2. Fill the tank. Run your garden hose from the spigot into the tank. Let it fill completely before you start the pressure washer. Do not try to fill and wash simultaneously from a low-flow source — the tank is there to pre-store the water.
3. Connect tank to washer. Run a short, kink-free hose from the tank outlet to the pressure washer inlet. Keep this hose as short as possible — every foot of hose adds friction and reduces flow. Use a filter screen at the tank outlet.
4. Prime the pump. Before you start the motor, squeeze the trigger gun with the nozzle pointed at the ground. Hold it for 10–15 seconds until a steady stream of water flows with no sputtering. This purges air from the line and prevents the pump from dry-starting.
5. Start washing. Once primed, start the motor and work normally. Monitor the tank level — if it runs dry, the pump will start to cycle again.

If gravity alone is not enough

Some setups — flat ground, long hose runs, or particularly low-flow sources — need a small booster pump between the buffer tank and the pressure washer inlet. A 12-volt booster pump costs $30–$60 and pushes water from the tank to the washer at a consistent rate. This is especially useful for remote locations where you cannot elevate the tank above the washer.

When a Buffer Tank Is Not the Answer

Here is when you should not buy a buffer tank:

• You have city water and a 3/4-inch hose. Municipal water typically delivers 5–8 GPM. If your washer is cycling with that supply, the problem is a clogged inlet filter, an air leak in the hose connections, or a faulty unloader valve — not water flow.
• You need higher performance than your machine delivers. If your washer is rated at 1,500 PSI and you need 2,400 PSI to strip stain from a concrete patio, no buffer tank will fix that. You need a different machine. The electric pressure washer category covers the full range of options by PSI and GPM.
• You are cleaning commercial spaces daily. A buffer tank is a workaround for residential limitations. If you are washing a parking lot five days a week, you need a direct water-line connection and a machine rated for that duty cycle — not a 35-gallon tank you have to refill every 20 minutes.
• It is winter and you are skipping storage prep. A buffer tank full of water in an unheated garage will freeze and crack. If you use a buffer tank, drain it completely before storing. Standing water in the tank and connecting lines still freezes — the tank does not protect itself or the washer from winter damage.

Know when the accessory solves the problem and when it does not. That is the difference between spending $50 wisely and spending $50 on something that sits in your garage next to a machine that still does not work right.

Frequently Asked Questions