Plus, the little paper tea bags change the flavor of the tea. Best bet is to buy loose tea. In a store, you might need to ask about age - try to find a local herbal shop. Try to get organic when possible. Herbs should be stored in an airtight container out of direct sunlight.
Fresh herbs are more potent than dried herbs.
The drying process can remove some of the essential oils. So if you premake a jug for your fridge, drink it in one day. When you heat the water, it is ready just as it begins to boil. Do not overboil because it causes water to deoxygenate. Just like with a glass of water left out overnight, your tea will have a flat taste.