What Is the Cut Off Point in a Fast Day?

There's a concept in jewish law about eating. How much food or drink do they have to take to be considered breaking their fast? And so, for example, your walking down the street and it's raining, and a drop of water ends up in your mouth. Did you just break your fast? Of course not. So that's a giisas a great saga. This ist that was melkas, always got the good saga.