Cut the watermelon into large chunks, removing seeds as needed, and measure out 4 cups of watermelon flesh.
Place the watermelon chunks into the blender jar, ensuring it's not overloaded. Add the freshly squeezed lemon juice to the blender.
Blend on high speed for about 30 seconds, until the mixture is smooth with a slightly pulpy texture. You should see a vibrant pink liquid with visible bits of watermelon pulp.
Place a fine-mesh strainer over a large bowl or pitcher and pour the blended mixture through it. Use the back of a spoon to gently press the pulp and extract as much liquid as possible, resulting in a clear, vibrant pink beverage.
If desired, add honey or sugar to taste and stir until fully dissolved. Adjust sweetness based on preference.
Transfer the lemonade to glasses filled with ice, garnish with lemon slices or fresh mint if desired, and serve immediately for a refreshing, chilled drink.
