Watermelon Lemonade

Squeeze lemons into a large pitcher; add squeezed lemon quarters. Add mint and sugar; mash with a wooden spoon until mint is bruised and sugar is dissolved.

In a blender, puree watermelon in batches until smooth; pour through a fine-mesh sieve into pitcher (you should have about 8 cups of juice). Stir to combine. (Refrigerate, covered, up to 3 days.) Add vodka, if using; serve over ice.