A typical gas or electric pressure washer pumps the water from a garden hose to a high pressure. The pressure washer is hooked to a high pressure hose that when the trigger is pulled the water mixes with air to come out of the nozzle. Typically the water comes out around 75 times that of a regular garden hose. Some pressure washers also have a detergent tank that will mix with the water so when they both come out of the hose at once. The high pressure not only cleans more effectively but wastes less water than a regular hose.