By taking the vitamins your body won't be able to go into a fasting mode.
This is where a number of functions of the body slow down or shut down as with the digestive system which needs to shut down.
If it doesn't shut down, as by taking things in addition to the water, the body won't make the transition over to living off its stores of nutrients and will only be living off of what is in the diet, this being the 50 or so calories you mentioned.
50 or so calories per day constitute a starvation diet where the body will burn vital tissue including muscle and organs for its sustenance.
I highly recommend the Water Fast and hope that I have been polite with my response.