re: To hold the water or to drain.

quote:

---

The way thermodynamics works when you start with all ice and it begins to melt the water/ice mixture is in equilibrium and the same temperature during the phase change only when all the ice is gone does the temperature of the water begin to rise.

---

This is true, and doesn't really address the question.

At the core this is a heat transfer and heat storage question. Heat loss is increased by the difference in temperature between two objects. So by draining the water the level of cold in your ice chest drops and the rate of heat loss decreases (less cold surface area). (A little bit - the air above the water is still pretty cold).

But the cold water has a MUCH higher capacity to retain the cold than the air above it in the chest. Easy answer - you keep the cold water in the chest.