A pressure washer is used to remove moss, mold, grime, mud, and dirt from various surfaces and objects by delivering a concentrated stream of water.  Pressure washers are available to rent by the day from home improvement stores for those who may only need to use one occasionally.  Otherwise, it is a useful tool for the homeowner to have on hand for cleaning decks, sidewalks/driveways, outdoor furniture, etc.

Video: How to Operate a Pressure Washer