I have been fasting on nothing but water almost 5 days now. I have no hunger pangs nor am I hungry. I still power walk at least 3miles daily, weight train, bike ride, raquetball, basketball, and running, with no ill effects. I have never gone beyond 3 days before (but also that was a fast with no food OR water). So, to just have water for almost 5 days is really amazing, and can be done.