You should try the hot water thing if you haven't actually done so. The cost is pretty much zero.

Have you tried filtering your water, or drinking it very cold? Water tastes like what's in it, and the taste varies depending on the source. Most city water tastes like the chemicals they use to clean it, while water from a cheap filter tastes like nothing. Cold water also seems to have less taste, or at least I've found I can't detect the taste of cold water (as in, with ice in it, not just cold from the tap).

Seltzer (Or whatever they called carbonated water in your part of the world) is another "almost-water" drink, much like tea. No calories, enough taste to notice, feels like soda.