In a small saucepan, combine sugar and 1 1/2 cups water; bring to a boil. Reduce heat and simmer until the sugar dissolves, 3 to 4 minutes. Remove from heat and cool completely.  In a large pitcher, combine lemon juice, 1 1/2 cups sugar syrup, and 4 cups cold water (add remaining sugar syrup to adjust sweetness, if desired). Refrigerate until chilled.