Cellular respiration — How is the water expelled?
Edited: I was wrong, the balance varies quite a bit by species. Reptiles and birds are far more water efficient than large mammals becasue they do not lose water through sweat or urine. There are animals that are metabolically water neutral, but humans are not one of them. In humans the water produced metabolically does far exceed the water used metabolically. I should have realized that reptile also produce less water. source 1source 2

In humans there are three main ways water is take in, drinking, injection (food), and a net metabolic production. There are four major losses, urine, sweat, respiration, and feces. so it is through one of these four methods.