As it gets hot outside (for those of you in the northern hemisphere), you need something cool to drink.
My enviro-suggestion is a water with essence drink. All you do is put a herbal tea bag in the bottom of your glass, throw some ice on top, pour on some tap water, wait 5 minutes, and stir. You can add sweetener if you like, though unsweetened works for me.
It has a more subtle flavor than iced tea. The tea bag will last for at least two fills.
I paid $2 for 25 peppermint tea bags at Big Lots a few days ago, so the total cost per 14-oz glass is maybe 10c, even if I factor in the cost of the electricity it took to make the ice. (If you really want to get technical, I rode my bike to the store, so there was no fuel cost either.)