dont do very much mobile work these days.. mostly only for existing clients. when I do, I always fill the water tank
power is a different issue. Although I carry a generator, I much prefer running a cord to clients power if possible for all the obvious reasons (cost, noise, etc)
I started carrying my own water a couple years ago and I feel it was so worth it. I HATED using clients water. Started with using clients hose upon arrival. The hose is kinked, it leaks, its in the mud, etc and you have the pleasure of hand coiling the dirty hose when you're done (you don't want to look like a slob)
ok I'll bring my own hose, and use their water. Rapid reel mounted on 2x4s with craftsman hose. Now I'm lugging around the thing on arrival. the reel is in their bushes. I'm still in the mud. etc etc
So much easier and so much more professional looking to flip open my tailgate, and fill buckets instantly. Is it necessary? No. But if you're doing this a lot it sure is convenient
45 gal tank
Flojet on demand pump
Optima marine battery (big boy size)
Rapid Reel
Craftsman hose
If I know the clients and I like how the water setup is, and I'm doing multiple cars, I'll use their water / my hose. Otherwise I fill the tank.
pressure washer is a must as noted earlier. I bring a small electric PW for mobile work.