Combine the water and herbs in a pot and bring to a boil. Reduce the heat and simmer for 20 minutes. Remove the pot from the heat and let the root and bark tea come to room temperature.
Strain out the herbs and put the tea into a wide mouth gallon jar.
Stir in the sugar, molasses, ginger bug, and ginger slices, then cover the jug with a piece of cheesecloth secured with a rubber band.
Put the jar in a quiet corner in your kitchen and let the root beer ferment. Give it a vigorous stir with a wooden spoon once per day. It should start to bubble up within 3-4 days, then it's ready to bottle.
Strain out the the ginger pieces and transfer the root beer to flip top bottles using a funnel, making sure to leave an inch or two of head space.
Let the bottles sit at room temperature to build up carbonation for at least a week before drinking your root beer. Serve cold and enjoy!
Many other herbs can be used to make homemade root beer, including wintergreen, licorice root, wild cherry bark, cloves, dandelion root, burdock root, juniper berries, and anise.