Bring the water and the tea bags to a boil in a large stockpot and let it simmer for about 15 minutes. You want the water to be a medium to dark brown.
Once the tea has simmered, remove the tea bags, and stir in the sugar or sugar substitute while the liquid is still hot. This will help the liquid take in the sweetener better, leaving a smoother taste and texture.
Add fresh squeezed lemon if desired.
Allow the tea to cool for at least 30 minutes at room temperature before transferring it to the fridge to finish cooling.
Serve over ice and add more fresh lemon if desired.
There are a lot of recipes that talk about boiling a smaller amount of liquid and then adding more liquid. This will cause the tea to be diluted, and you DON'T want that.