Step 1: To make the simple syrup, combine 1 cup of granulated sugar and 1 cup of water in a small saucepan. Heat over medium heat, stirring occasionally, until the sugar is completely dissolved. Remove from heat and let cool completely to room temperature.
Step 2: While the simple syrup cools, prepare the limes. Roll 8-10 fresh limes firmly on a countertop to help release their juices. Cut each lime in half and use a citrus reamer or hand juicer to extract about 1.5 cups of fresh lime juice. Strain the juice to remove any seeds or excessive pulp.
Step 3: In a large pitcher (at least 2-quart capacity), combine the cooled simple syrup and the fresh lime juice. Stir well until thoroughly mixed.
Step 4: Add 4 cups of cold water to the mixture. Stir again until everything is well combined. Taste the limeade and adjust sweetness or tartness as desired by adding more simple syrup, lime juice, or water.
Step 5: For best results, chill the homemade limeade in the refrigerator for at least 30 minutes before serving. Serve over ice, garnished with fresh lime slices and a sprig of mint, if desired. Enjoy your refreshing classic limeade!