Step 1

Zest 1 lemon into large pieces using a knife. Place lemon zest in a saucepan; top with 1 cup water and sugar. Bring lemon zest mixture to a boil, stirring occasionally, until sugar dissolves and liquid is syrupy, 5 to 10 minutes. Remove saucepan from heat and cool; remove and discard lemon zest.

Step 2

Stir lemon juice and vodka together in a pitcher; pour in lemon syrup. Stir in enough water to fill the pitcher.

Step 3

Fill glasses with ice; pour hard lemonade into each glass. Garnish each glass with a lemon slice.