I was addicted to coffee for many years, and within 5 days of water only fast, I no longer desired to drink coffee. I had terrible headaches, but they did pass. Prior to water fasting, I rarely ever drank plain water, I would only drink coffee, sweetened tea or soda. I have tried to drink a glass of sweetened tea recently, and it actually made me feel more thirsty. I never would've thought that water would become my first choice of drink today.
Water fasting can also help with nicotene addiction. Within a five day water only fast, the physical cravings were gone, but the mental/oral fixation to smoking were still there. I do breathing exercises(as if I was deeply inhaling a puff of a cigarette) and EFT. All of those things have helped more than anything I have tried in the past.