At least in my Keurig: there are 2 tanks, 1 external, 1 internal. There is a float in the external tank that detects if there is enough water in the external to

At least in my Keurig: there are 2 tanks, 1 external, 1 internal. There is a float in the external tank that detects if there is enough water in the external to fill up the internal. If so, then it brews the internal tank and then fills it up from the external after the coffee is made. If there is not enough water to fill up the tank, it won't start.