Heat 1 cup of water in a small saucepan over medium heat. When water is hot (but not boiling), add in sugar, stirring constantly until sugar is fully dissolved.
Remove from heat and allow to cool for 15 minutes.
Mix 5 cups of cold water and lemon juice in a pitcher. Add the simple syrup and stir until completely blended. Serve in a glass over ice. Store in refrigerator for up to 7 days.
Notes
Pink Strawberry Lemonade Variation: Add 1 cup pureed strawberries into the pitcher with the lemonade. Add ice to individual serving glasses rather than to the pitcher. When ice is added to the pitcher, it dilutes the lemonade as it melts.