What is the cooling rate of water?

The answer to this question depends on several factors. First, what is the volume of the water, and what shape is the container? Two gallons of water in the same shaped container as a gallon of water will cool at a slower rate. A gallon of water in a cube will cool more slowly than a gallon of water in a flat tray, because the water will exchange heat with its surroundings at the surfaces, and the water in the tray will have a much higher surface to volume ratio. Also, you really haven't defined hot and cool in your question. Once you do define those aspects, you have to also define what the surrounding temperature of the air or fluid into which the hot or cold water's container is placed. You'd also want to know the altitude, since that will affect the rate of heat exchange as well. So, there really is no answer to this question, except the empirical answer that you can get by just putting a thermometer in the hot water and watching the time it takes to reach your desired cool temperature.