My first instinct is to go to the tap. I've been drinking tap water for years and years, no problems whatsoever. Only time I won't prefer it is if the water from the tap tastes funny (I had forgotten about this, but I suddenly remember my grandmother's old place and her weird-tasting tap water...tasted sandy or something, it was so odd), but even then I would still drink it if I need to.
I'll drink other kinds, although bottles tend to be a "if they're the only things around" kind of deal, since I don't buy them myself.