I have one customer that I am allowed to use their water, but for every other customer I bring water to site. Every contractor that I know carries water with them to site and fills up at the city bulk water fills.
The one customer that I do take water from I only do if I run out, or they are in a hurry and I don't have time to fill before I get there.
Having a water tank means you can work anytime any where. When the temperature drops up here, outside taps don't exactly work any more. Although in warmer climates I am sure you don't have to worry about that too much.
Just my 2 cents
Benjamin