Its not a good  idea.. its has its complications  ...

First of all why you are on water fast? One cannot avoid water for long. If you are doing this for loosing weight it , don't do it. The lost weight will come back. To loose weight reduction in quantity of food , avoiding fatty , fast foods is must. It advisable to consult a dietician. Don't skip breakfast or dinner , must have food 3 times daily. Most importantly regular physical exercises are a must

Don't do this. Take adequate diet and do free hand exercise