Humanity's oldest dream of leaving Earth and building anew among the stars meets one of its oldest constraints: the availability of water. Elon Musk's vision of a self-sustaining lunar city within a decade has captured imaginations, but scientists studying the moon's hydrology are offering a sobering counterpoint — the ice locked in polar craters and scattered across the regolith is real, yet finite, and the arithmetic of survival does not bend to ambition. What is unfolding is not a rejection of the dream, but a reckoning with the difference between what we wish the universe to offer and what