Start by squeezing out the juice of your fresh lemons using a lemon squeezer.
Next, start to puree the watermelon and pour the contents into a strainer when done.
In a sauce pan, add the sugar and a 1/2 cup of water heating in on medium heat until the sugar dissolves (about 5 minutes or so). This will be the base of your lemonade.

Remove it from the heat. Stir in the other 3 cups of cold water and the freshly squeezed lemon juice.

Divide the ice between 12 glasses and add about 3 tablespoons of the watermelon puree first, then top with the lemonade.

Gently stir it before serving.