I use pressure washers a lot for work coating roofs & waterproofing concrete walls & decks. There’s one thing that no one thinks of that is every bit as important as psi, and that is gallons per minute of water use. The best washers that clean the best use 4 gallons per minute. The reason is the lower gallons per minute washers don’t wash the dirt away after it’s lifted from the driveway. Most hie bibs will flow at 8 gallons per minute w/o a hose on, so you’re still saving 1/2 the water.