Start by cutting the watermelon into cubes and removing any seeds if necessary. Place the chilled watermelon pieces into a blender. Blend until completely smooth and juicy.
Position a fine mesh strainer over a bowl and pour the blended watermelon through it. This removes excess pulp and creates a smoother lemonade texture. Press gently with a spoon to extract as much juice as possible.
In a large pitcher, combine the cold water, freshly squeezed lemon juice, and sugar. Stir continuously until the sugar fully dissolves into the liquid. This creates the sweet-tart lemonade foundation.
Pour the strained watermelon juice into the pitcher with the lemonade mixture. Stir everything together thoroughly until the color becomes evenly pink and vibrant.
Place the pitcher in the refrigerator for at least 30 minutes if you have time. Chilling allows the flavors to blend together and makes the drink even more refreshing.
Fill serving glasses with ice cubes. Pour the watermelon lemonade over the ice and garnish with fresh mint leaves, lemon slices, or watermelon wedges. Serve immediately and enjoy.