In a small saucepan, combine 1 cup water with 1 1/2 cups sugar.
Place over medium heat and bring just to a simmer, stirring to dissolve the sugar.
Remove from the heat and let the syrup cool to room temperature. Pop in the refrigerator for it to cool faster.
Squeeze 1 1/2 cups lemon juice.
To make the full batch of lemonade, pour 7 cups cold water into a pitcher. Add the 1 1/2 cups of lemon juice and 1 1/2 cups chilled sugar syrup and stir to combine. You can also add the lemon juice and sugar syrup to taste.
Add ice to glasses when serving.
Garnish with lemon slices.