I thought you don't need high pressure water from a tap, but the pressure washer creates the pressure itself? I don't have to turn my outside tap on by much, once there's enough water in the pressure washer it starts working and the tap is just to keep it topped up constantly.
it's not like a hose where it would just dribble out the end as that's just feeding the water from one place to another with no pressurising involved, or I'm just talking rubbish