Make the simple syrup: In a 3-quart saucier, combine the sugar and water. Slowly bring to a boil over medium heat, stirring occasionally. At this point, the simple syrup can be cooled and stored in anairtight container in the refrigerator for 1 month. For infused syrup, remove the pan from the heat and add the sliced lemons and sprigs of fresh mint. Cover, steep for 10 minutes, strain, and store as you would simple syrup.
Make the tea: Bring the quart of cold water to a boil over medium-high heat in a kettle or small saucepan.
In a large, heat-resistant container, pour the boiling water over the loose tea and let steep for 4 to 5 minutes. Strain the tea into the room-temperature water in a large pitcher. Serve over ice, sweetened with simple syrup, if desired.