Make simple syrup first: Mix together the sugar and water, and bring to a boil. Allow it to boil for 2 minutes, then set aside to cool. Mix together the 5 cups of water, tea bags and zest. Stir and pour into a large, clear jug. Place the mixture in a sunny window or cover the jug and place it in direct sunlight outdoors. Allow it to sit for about 4 hours, stirring occasionally. Remove the tea bags and squeeze the excess tea into the jug. Add the lemon juice and 1 cup of the sugar syrup you made earlier. Mix well (you can keep remaining syrup in a mason jar in the fridge for later use). Yield: approx. 2.5L