Wash one lemon to remove any waxy coating. Trim the hard stem end; cut into quarters and remove the seeds.
Juice the other lemons.
In a blender, combine the lemon juice, cut lemon, fresh mint leaves, sugar, and 1 cup of water.
Blend or process until the mint leaves are finely chopped, and the sugar is dissolved.
Strain the mixture through a fine mesh strainer to remove any solids and transfer the liquid to a pitcher.
Add the remaining 3 cups of cold water to the pitcher and stir well to combine.
Taste the Limonana and adjust the sweetness and tartness with more sugar or lemon juice, if desired.
Fill glasses with ice cubes and pour the Limonana over the ice.
Garnish with additional fresh mint leaves and lemon slices, if desired.
Serve the Limonana immediately and enjoy!