tea bags (especially herbal, but any) also work great. I use one tea bag in a 20 oz bottle of water, so even if it's caffinated, it's very very veyr weak!
In the summer, two of my favorite drinks are:
1) spa water - take parsley, cucombers, and squeeze a lime into a 1 quart pitcher then chill. pour (I use a strainer) and drink. tastes like drinking grass. you'll think it's wierd, till you try!
2) rasperry and cinnimon water - add one cup crushed rasperries (make sure to eat them, or it's not as healthy) and 1 teaspoon of cinimon to 1/2 quart of water. delicious!
3) rose water - this is new for me. Make regular tea (i make mine weak, to spread out the caffine), and add 1 tablesppon of rose water. god, this is good!