Try this little experiment - go outside and turn on your water faucet.
In one minute, 8 gallons of water will pour out of your hose.
Now, attach a spray gun to your garden hose.
You basically reduce the flow to about 5 gallons per minute. As a result, the water pressure increases from 10 PSI (pounds per square inch) to 40 PSI.
This increases the pressure by 4 times and simultaneously reduces the amount of water used. However, the water pressure isn’t strong enough to actually clean anything. It just pushes stuff around and gets your socks wet.
A pressure washer takes the same principle to the extreme; it uses a gas-powered engine or an electric motor to boost water pressure to 1000-4000 PSI. We’re talking about serious water pressure that can actually clean stuff.