Tasty [healthy] beverage

I work at home and by happenstance there is a dollar store one minute away which sells pop/soda at a cheap price. This has led to quick temptations while programming and reading.

Does anybody have any recommendations for a tasty, healthy beverage as a substitute for pop? Aquafina Vitamin Waters (no, not the Glaceau ones which are ironically not very healthy) are a great alternative but they're not commonly available and unless on sale, aren't cheap.

Location: Canadia.