Tom Bosley -- who famously played Mr. Cunningham on  Happy Days  -- died this morning at a hospital in Rancho Mirage, CA ...
Average estimates: $250 to $420. Power washers can have pressures of 4,000 psi (pounds per square inch) to lesser pressures of maybe a few hundred and run by gas or electric. This means that professionals will probably use one with less pressure to clean a deck and maybe one with higher pressure to clean a patio.
Water: according to Elements, a professional pressure washer of 1500 PSI uses approximately 10-15 gallons per minute. The American Water Works Association places the price of 1000 gallons of water at $1.50, placing the estimated cost at $2.40-$8.10.