How much flow rate do I need?

The amount of pressure available to you tends to increase as you move up the range of pressure washers and the Flow rate increases to match it.

If you buy a washer with 100 bar of pressure for example, it may have a flow rate of perhaps 340 LPH and perhaps a model with 135 bar may have a flow rate of 500 LPH. 

 

N.B. The pressure bar rating stated is often a maximum, as many pressure washers allow you to change the flow rate up to the top rate, e.g. 10-110 bar of pressure