Use a ceramic juicer or handheld juice to squeeze your lemons. You need at least 1 cup of lemon juice and the 5-6 lemons should get you there. If you want to add more lemon juice you will get more of the sour lemon flavor in the final drink. Set aside when done.
Cut a watermelon in half and add it to a bowl. Blend the watermelon, in phases if needs be, until it's a liquid.
Strain the watermelon mixture in order to get all the pulp out of it. You want to discard the pulp (or feed it to your chickens). Use only the watermelon juice. You will need it to make 4 cups.
Combine strained watermelon juice and fresh squeezed lemon juice in a pitcher.
Add in your sugar and water. Mix well until the sugar is dissolved.
Serve over ice and garnish with your mint.