Nutritional experts tell us all the time to “stay well hydrated.” This means: keep introducing fluid into our bodies. It is sensible advice but it raises the question: what kind of “fluid” counts? Water is good of course: it is the paradigm of hydration. But: what about coffee?
There is an urban myth that coffee doesn’t serve as hydration because it is a diuretic: that is, it will send you to empty your bladder pretty quickly. As a consequence (says the myth) coffee actually has a net negative consequence for the cause of hydration It dries you out.
This, though, is false. Doctors say that even after the diuretic effect is accounted for, there is a net position hydrating effect from drinking coffee. Specifically, for each 8 ounce cup of coffee you drink, you can count only 7 of those ounces toward your fluid intake for the day.
In Pill Form:
If you are conscious of your hydration day to day, and you have quantitative goals to that end, then simply using water is the best way of getting there. But if you have a cup (or three) of coffee in the morning, feel free to count a portion of that toward the overall hydration goal.
Be mindful that, as with almost anything, it is possible to enjoy coffee to excess. It is generally best to switch to decaf later in the day.