I drink nothing but water and still have no energy?

See your doctor: There are many things that can cause a lack of energy or fatigue. This can include anemia, thyroid disorders, diabetes, etc. Best to see your doctor to determine the cause and provide you with a treatment plan.

Only water?: But surely, you must already know that it is not at all healthy to only drink water? I mean, come on now. If you don't actually eat any food, you should know why you have low energy.