The big market for bottled water baffles me as well, but so does any claim suggesting that any drinkable water pretty much tastes the same. Whenever I go travelling I drink the tapwater as long as it's considered safe, but it also reminds me that it generally tastes better (as in less treated) at home and I pay the city's utility bill with pleasure. Not even to mention drinking straight out of a pristine stream when hiking on a hot day and the water is just barely above freezing temperature. In the latter case I do admit that the total experience, the sceneray and all may play a big part in the equation.
As a side note - the various local variations on the lager beer style (Czech, german, vienna lager etcetc) are historically at least in part a consequence of differences in the local water chemistry. These days one can easily brew any style pretty much anywhere by adding minerals, but water isn't created equal just because it's wet everywhere.
I pretty much always carry a plastic bottle and fill it when convenient. Paying top money for bottled water is way beyond me.