1In blender, place watermelon. Cover; blend on medium speed about 45 seconds or until smooth. Strain through fine mesh strainer into 2-quart or larger pitcher.
2Squeeze juice from lemons and limes; add to watermelon puree. Stir in cold water and sugar. Refrigerate 1 hour.
3Stir before serving. Serve over ice. Garnish with watermelon slice.