Use a knife to cut off the ends of the lemon. Then slice away all of the lemon peel, leaving only the lemon flesh. Cut this into chunks, removing any seeds.
Slice the watermelon and remove the white and green rind. Cut the watermelon into small pieces.
Add the lemon chunks, watermelon pieces, and the sugar to a blender.
Blend for about one minute, until the lemon is completely blended and the sugar is well dissolved. Transfer the puree to a serving pitcher.
Add 16 ounces (2 cups) of water. Stir the lemonade well and serve over ice.
Nutrition facts are sometimes provided below and are calculated using an online calculator. With specific brands of ingredients and additions, omissions, or substitutions the nutrition facts may change. We encourage you to use your own nutrition facts calculator to obtain the most accurate nutrition facts for your meal.