In a saucepan, heat 1 cup of water and granulated sugar on medium heat. Cook just until the sugar dissolves. Remove heat and allow it to cool. (You can also use hot water from a tea kettle to dissolve the sugar.)
1 cup granulated sugar, or other sweetener
Cut the lemons in half and juice the lemons into a bowl or measuring cup with a juicer or hand squeezer. (Remove any seeds from the lemon juice.)
1 1/2 cups lemon juice, about 8-10 lemons
Add the rest of the water, cooled simply syrup and lemon juice to a pitcher and stir until well combined. (Adjust the lemonade if you want it to be sweeter or more on the sour side.)
6 cups water
Add the watermelon chunks, mint leaves, and water to a blender and blend until pureed.
5 cups fresh watermelon, cubed, 1/4 cup water, 4 mint leaves, optional
Place a strainer over a bowl or measuring cup and strain the puree. (Or just strain straight into the pitcher to avoid more dishes.)
Pour in the watermelon juice into the pitcher of lemonade and mix to combine.
Add ice cubes, mint leaves, and additional lemon and strawberry slices to the pitcher, stir to combine and serve.