Pressure Washer Water Supply Requirements

1. What Your Machine Actually Needs

The rule is simple: the tap must supply at least as much water as the pump is rated to move, and preferably more. A machine rated at 2.0 GPM needs a spigot that can deliver 2.0 GPM through the hose you have attached to it, not in theory but at the moment the trigger is pulled.

Headroom matters more than the bare minimum, because supply is not constant. A toilet filling indoors, an irrigation zone opening, or a neighbour's demand on a shared line all pull the available flow down briefly, and a pump running with no margin is the one that draws air when that happens.

Pressure at the tap matters much less than flow. Most machines are happy with normal household supply pressure, and a few specify a minimum around 20 PSI. What they cannot tolerate is a supply that delivers the pressure but not the volume, which is exactly what a long thin hose produces.

2. The Bucket Test

You do not need a flow meter. Two minutes with a bucket tells you whether your supply can feed the machine you own or the machine you are about to buy.

• Attach the garden hose you actually intend to use, at the full length you intend to use it.
• Open the spigot all the way, not most of the way.
• Time how long it takes to fill a five-gallon bucket.
• Divide five by the minutes taken. Two and a half minutes is 2 GPM; five minutes is 1 GPM.
• Repeat with the hose disconnected, straight from the spigot, to see how much the hose is costing you.
• If the two figures differ a lot, the hose is the restriction, not the plumbing.

3. The Hose Is Usually the Problem

Householders blame the plumbing and it is almost always the hose. Bore diameter and length together decide how much of the tap's flow actually arrives at the machine.

Use a 5/8-inch or 3/4-inch hose no longer than about 25 feet, connected to a spigot opened all the way. That single sentence prevents most water-side pump failures, and it is the setup detail people most often get wrong because a longer hose is more convenient.

Expandable and coiled hoses deserve particular caution here. They are excellent for watering and frequently have a narrow internal bore, which is fine for a sprinkler and marginal for a pump that wants two gallons a minute. If you use one, run the bucket test with that hose attached before trusting it. Our guide to garden hoses covers bore and flow in detail.

Kinks Are Invisible and Instant

A kink does not reduce flow gradually; it stops it. Because it usually happens behind you while you work, the first sign is the machine beginning to pulse. If pressure suddenly becomes inconsistent mid-job, look at the supply hose before anything else, because it is the most common cause and the easiest to fix.

4. Cavitation: How a Starved Pump Dies

This is the failure mode behind most dead consumer pumps, and knowing what it sounds like lets you stop it before it does permanent damage.

When the supply cannot deliver the volume the pump wants, the pump pulls a partial vacuum and water vaporises at low pressure inside it. Those vapour bubbles then collapse violently as they reach the high-pressure side. Each collapse is a tiny, extremely localised impact, and millions of them erode seals, valves and pistons.

• The symptom is pulsing: pressure that surges and drops rhythmically rather than holding steady.
• It often sounds rougher and rattlier than normal running, as if the machine is passing gravel.
• It is frequently mistaken for a worn pump or a failing motor, which leads people to replace working machines.
• It happens fastest on high-flow machines, which have the least tolerance for a marginal supply.
• The damage is cumulative and permanent, so a machine run this way for a season does not recover.
• Nearly every cause is on the supply side and costs nothing to fix.

5. The Inlet Screen Nobody Cleans

There is a small filter at the water inlet of every pressure washer. It catches grit that would otherwise reach the pump, and it clogs gradually over a season with sediment, hose debris and whatever was living in the spigot.

A partially blocked screen starves the pump with no symptom other than reduced pressure, which people almost always blame on the machine wearing out. It is the single most common maintenance item on an electric pressure washer and the one least likely to be done, because most owners do not know the screen exists.

• Pull the screen out of the inlet fitting, usually with needle-nose pliers or a small hook.
• Rinse it under a tap from the clean side outward, and use a soft brush if there is scale.
• Hold it up to the light. If any part looks blocked, keep going or replace it.
• Refit it the right way round; it is directional on some machines.
• Do this a few times each season, and always after drawing water from anything untreated.
• Replace it if it is torn, because a torn screen lets grit through and grit is what it was fitted to stop.

If you draw from a water butt, a pond or a bucket with a cordless machine's siphon hose, the screen matters far more. Keep the intake off the bottom of whatever you are drawing from so it does not lift sediment, and rinse the filter after every session rather than a few times a season.

6. The Startup and Shutdown Sequence

The order of operations matters as much as the equipment. Two habits here account for a large share of the difference between a pump that lasts a decade and one that lasts two seasons.

Turn the water on before starting the machine. Starting a pump dry, even briefly, damages the seals, because they rely on water for both lubrication and cooling. Connect the hose, open the spigot fully, then squeeze the trigger to purge air from the system until water flows steadily from the wand, and only then switch the machine on.

Do not run in bypass. With the machine on and the trigger released, water circulates inside the pump and heats up rapidly, and sustained bypass is the leading cause of pump failure across every kind of pressure washer ever built. A Total Stop System shuts the machine off automatically when you release the trigger, which is why it is a feature worth insisting on.

• Connect the supply hose and open the spigot fully before touching the switch.
• Squeeze the trigger and let water run through the wand until the flow is steady and free of air.
• Switch the machine on, then fit the nozzle you want.
• If you pause for more than a minute, switch off rather than leaving it in bypass.
• At the end, switch off, close the spigot, then squeeze the trigger to release trapped pressure.
• Disconnect the hoses and drain them, and drain the machine before storing it.

That final release of trapped pressure is worth the two seconds. A high-pressure hose left pressurised puts a standing load on seals and fittings, and disconnecting under pressure is how people get hurt by a fitting letting go. It also makes the hose far easier to coil.

7. Cleaning Where There Is No Tap

Corded electric machines generally need a pressurised supply and cannot draw from an open source. That is a genuine constraint rather than a preference, and there are three ways around it.

A five-gallon bucket is a meaningful amount of cleaning at these flow rates, enough for a bike, a set of chairs or a muddy dog, and it can be refilled anywhere. It is not enough for a driveway, and no siphon setup changes that arithmetic.

Check the machine's own manual before rigging anything. Some units explicitly forbid gravity or siphon feed, and running one that way will starve the pump exactly as a blocked screen would. Our comparison of cordless versus corded machines covers which formats genuinely support drawing from open water.