Depends on what time of year I'm camping. Come the summer, the FW tank and ice are good enough.
Winter, when I'm camping in the unpredictable Texas weather that can be sitting at 90 degrees one day in February... several days later, a hard freeze hits, and the high may be in the low 30s for a week or so.
I use water bottles in the winter for a few reasons. If they freeze, they tend not to burst or leak, so I can leave them in my TT's refrigerator. Plus, I can also use frozen ones with my hard-sided gel packs to pre-chill my fridge when turning it on, come Friday.
I do have one caveat about bottled water: I always buy the stuff that is bottled from a tap. Not spring water (where water rights are being fought over), but from local tap water, or a place outside of Austin that uses filtered rain water for their bottles. I don't like using bottled water, so I try to minimize the impact done.