I try to mix it up. I'm concerned that if I stick to 1 source, I'll be contaminated by high levels of organic chemicals, heavy metals, manganese (a lot of people don't even know what that is) or something else particular to that brand. Often, the choice is dependent more upon image than taste (same as vodka).

I avoid the tap in LA, but not when I'm visiting NYC.

I remember in Cambridge, MA seeing the source of a leading (but not posh) brand of spring water being pumped up from the middle of an industrial park.