TMC welcome to the PWI board.
Your question would be better suited to be in a different forum and your responses will be better. I am unable to move the post, but you might want to re-ask in the power washing area.
cleaning is cosmetic and i do have a recovery system for run off. i usually charge hourly but have a customer that would like a bid for 10.6 miles of curbing
Have you determined how many feet of curb you can wash on one tank of water? Managing water is going to be your biggest challenge.
Perhaps you should go to the back of a shopping center somewhere and wash a hundred feet of curbing to get a grip on how long this job is going to take. Once you have that info, you can create a decent bid.