Water volume output is the component of cleaning that gives the ability to flush away dirt and grime. It is the component most overlooked in pressure washers. Without adequate water volume the output pressure of a washer would be useless. As an example of an extreme case, if you had a washer capable of producing 3000 PSI but at only one quarter gallon per minute (GPM), it would only be suitable for pinpoint etching at close proximity. Depending on the application, 2000 PSI @ 4 GPM could provide better cleaning performance then 3000 PSI @ 3.2 GPM.

Water volume outputs normally range from 1.3 GPM on the low end of the scale to 20 to 30 GPM at the very high end of the range.

For average washing applications it is best to stay above a minimum of 1.8 GPM and there is little need in most cases for much more than 5 GPM.