I wanted to do a water fast for the whole month of Ramadan but I'm not sure if it is allowed to not eat at all. So I would break my fast with water instead of food.
For breaking the fast you only need to eat or drink something or have a (halal) physical relation. So yes it would be acceptable and technically correct (fiqh perspective) to break fast by only drinking water. But you won't be following the sunnah by eating at least some dates etc. and I doubt that it would be good for your health to do this a longer time.