Try this one. You can tinker with it to adjust the tartness/sweetness of it by changing the sugar amount. Steeping the thin lemon slices extracts the lemon oil in the peel and imparts a nice lemony flavor.
1 cup freshly squeezed lemon juice, including pulp (remove seeds)
¾ cup granulated sugar
4 cups spring water
Slice one of the lemons very, very thin (seeds removed) and set aside. In a small saucepan, combine the sugar and ¾ cup of the water. Stir over medium heat until the sugar dissolves and you are left with a simple syrup. Remove from heat and stir in the thinly sliced lemon. Cover and refrigerate until fully chilled.
To serve, strain the chilled lemon syrup into a large pitcher, add the lemon juice, remaining water and the second lemon that has been cut into ¼-inch slices. Stir well and pour over ice.