Hi Dave
Ive read all of the replies you have had so far.
what you really need to do is survey which of your customers have a tap, and plan from there.
As for the point of customers turning off their water supply in the winter, the only way you will know about that is to ask them, none of my customers do this.
a good point was made about transporting the di bottle on a trolley, I use a £25 foldaway job from B & Q for this, my hosereel attaches to it as well.
What method you use really depends on the your type of work, I have 2 very large private estates where I can plug into someones tap and maybe do 2 or three houses before wheeling the trolley to the next tap.
The hose has 25 feet 1/2 hose attached to 150 feet of winspray hose so I can reach quite a distance.
As i said before, a cheap way of seeing if wfp is the way to go for your business
Ian