Cut the blackened root end off of the end of the lemongrass stalks. Rinse the lemongrass under the tap to clean it. Cut the stalks in half. Crush the stalks gently with the back of a cleaver or chopping knife to help release the juices.
Add the lemongrass to a pot of water at a proportion of roughly 1 cup of water per 1.5 oz. of leaves. Place the pot on the stove and set the burner to high. When the water comes to a boil, reduce heat and simmer for 90 minutes to 8 hours, depending on how strong you wish the flavor to be.
Strain the juice into a pitcher. Throw away the leaves.
Add sugar or artificial sweetener to taste. Drink hot or chill and serve cold.