Roll lemons firmly on the counter to loosen the juice.

Slice lemons lengthwise and squeeze until you have 1 cup of juice, removing seeds.

In a small saucepan, combine 1 cup sugar and 1 cup water over medium heat.

Stir until the sugar is completely dissolved to create a simple syrup, about 3 to 5 minutes.

Remove the simple syrup from heat and let it cool slightly.

In a large pitcher, combine the lemon juice, simple syrup, and 4 cups cold water.

Stir well until everything is evenly mixed.

Taste and adjust sweetness or tartness if needed by adding more sugar or lemon juice.

Refrigerate for at least 1 hour to chill.

Serve over ice with optional lemon slices for garnish.