Thirding the carbonated water—I also have a SodaStream and love home carbonation. I add a few drops of concentrated sugar-free juice (pomegranate, cranberry) or a spritz of citrus.
You can also do flavored waters in a pitcher in the fridge. Just a few slices of cucumber, grapefruit, mango, apple, pineapple, etc. is enough to give a whole pitcher of water a great zing. Many herbs are great for this, too—mint, rosemary, and basil are my favorites.
If you do dairy, steeping some herbs (cinnamon stick, star anise, cardamom, cloves, allspice berries) in it and adding some vanilla extract is a great warm wintery drink.