You do need a license to do pressure washing in California.
In order to setup a pressuring washing business in California you have to get a pressure washing license through the state of California's state contractors state license board.
The pressure washing license will require you to be at least 18 years of age and have 4 years of journeyman experience.
Pressure washing companies do not use their own water if there is water on site.
Most pressure washing companies will use the customers water and water spigot for their pressure washer.
However some pressure washing companies bring water with them in large water storage tanks.
The water used by the pressure washing company for residential places is not all that much or that costly.
When I hired a pressure washing company to pressure wash my driveway and house they used my water which was okay.
The water bill didn't go up by much and was only maybe $2.00 more.
Most standard pressure washers will use between 2 to 4 GPM.”
That comes a total of 120 to 240 Gallons Per Hour.
To bring that into perspective, a standard bathtub holds about 80 gallons of water.
If you were to clean your house for 1 hour straight, you'd be using the equivalent of about 2 to 3 baths.