The only thing I will add to water sometimes is those little Crystal Light packets, usually lemonade flavored, because I love me some lemonade. I've tried the other kinds of water enhancers but the flavors always tasted a little off to me. Or, it tastes weird because it's like really watered down juice.
I enjoy drinking water by itself usually, though I want it to be ice cold (preferably crushed ice). Room temperature beverages are no good.