It is a long-established myth that we need at least eight glasses of water a day to stay hydrated. Our daily fluid intake covers virtually any non-alcoholic beverage including tea and coffee. Those two drinks have a diuretic effect as well, but not enough to alter the balance between drinking liquid and losing liquids through the kidneys. In fact, decaf coffee is even better because it provides hydration without any diuretic effect. Of course, water is still the best for daily fluid intake but decaf certainly helps.