How would you feel if somebody told you that you are little more than just a bunch of salt water? Well, it’s almost true–we and our favorite companion, the horse, are approximately 60% (by body weight) salty water. So now, with the help of a little arithmetic, we can calculate the following: A generic adult horse (named Salty) weighing 450 kilograms (990 pounds) multiplied times the 60% gives us 270 kilograms of water! Great, but what kind of volume are we talking about? The real question is, how much does water weigh? The easy way to remember this is the rhyme used by many a student : "A pint’s a pound the world around." So, a quart weighs two pounds, and therefore a gallon is eight pounds, which is equal to 3.6 kilograms.

With that information, we see that there are approximately 75 gallons or 283 liters of water to a horse (total body water). Now, as sore a subject as the metric system is in America (we seem to have stalled out somewhere in the middle of adopting it), we will talk from this point on in those terms. The only thing to remember is that a liter is almost a quart (0.946 of one to be exact), and that a kilogram is about two pounds (2.2 to be exact).

The Body’s Water

With that bookkeeping out of the way, it becomes more complicated. The total body water is essentially divided in two compartments–the intracellular fluid compartment and the extracellular fluid compartment