Prepare Citrus: Wash and scrub the oranges and lemons under cool running water. Zest half the orange and one lemon, then juice the fruits until you have the required amounts.

Make Citrus Syrup: In a small saucepan, combine granulated sugar and one cup of water, heating over medium heat until the sugar dissolves. Mix in the orange and lemon zests and allow to cool.

Combine Ingredients: Strain the citrus syrup into a large pitcher, add orange juice, lemon juice, and three cups of additional water. Stir well.

Serve: Fill glasses with ice and pour the lemonade mixture over. Garnish each serving with slices of orange and lemon.