[@Wraithblade6] I tried making it as common sense as I could, weighing out how much, statistically, a human needs to drink water each day to stay alive or at least survive, and weigh it against the scenario for vampires. 
Maybe it will help to say..
You can go days without any blood, but it would at least require a week to feed, and after would entail hunger, & progressively, starvation. Your (human)doctor will tell you whats needed to stay at peak performance, but it takes time to really become a problem. 
Does that make sense? For vampires it will take a longer amount of time. 
I did, in fact, want the blood to be a pressing issue for the vampires. I'll go in and try to arrange something that's more sensible and clear. 

Ps. Of course, starvation may not actually kill the vampire, just a very painful/immobile experience. 

Does this help you?