Ah, the sweet pink taste of summer. Perhaps my favorite two-ingredient recipe: Watermelon Agua Fresca. Popular in Mexico, any number of fruits could be used. One of my housemates during college made this watermelon agua several times during one long, hot Portland summer. It doesn't get much simpler or more refreshing than this.
I. Chunks of watermelon, just covered with water, blended well.
II. Refrigerate and serve, diluting with additional water, to taste.
(My preference is about 50% watermelon juice and 50% water.)
This is one of those times when you "pulp-free OJ people" might want to strain it. You'll still be left with lovely pink fresh water that is soooo much better (healthier and more delicious) than any kool-aid or commercial flavored beverage. But give it a try without the extra step and extra mess of straining, and you'll get the benefit of a little fiber in there, too. For those of you who are already juicing all the time, give yourself a break; hold the mint and protein powder, and cucumber-kale-ginseng... etc. Just relax: watermelon and water. I'm telling you.