Watermelon mocktails taste best with fresh, in-season watermelon, so selecting a ripe melon is essential. Look for a melon with a strong, consistent stripe pattern. The stripes should be a deep, dark green, while the pale stripes should be a creamy, light yellow. Give the melon a gentle tap and listen to the sound it makes. If the pitch sounds deep and hollow, then the fruit has more water and is likely riper. A higher-pitch sound can indicate a thicker rind and an unripe melon. Select a melon that is heavy for its size. Pick a piece of pre-cut melon if you prefer to see the flesh.