Cooling the Cloud dismantles the myth that modern computation is weightless, clean, or detached from the physical world. Every search, model run, and AI workload produces heat. At scale, that heat cannot be wished away, optimized out, or abstracted behind software. It has to be removed, continuously, under all conditions. This book follows that heat from the processor to the cooling system, from liquid loops to evaporation, and finally into the tributaries, aquifers, and watersheds that absorb the cost. With technical clarity and restraint, Cooling the Cloud explains why air cooling fails at high density, why liquid systems inevitably converge on evaporative heat rejection, and why continuous water withdrawal destabilizes headwater regions long before damage becomes visible. It shows how permitting, incentives, and sustainability metrics hide physical loss until recovery is no longer possible. This is not a book about speculative futures or symbolic sustainability. It is an examination of how digital infrastructure interacts with real hydrology, real limits, and real communities. For engineers, planners, policymakers, and anyone who wants to understand what the cloud is actually made of, Cooling the Cloud offers a necessary and unsettling account of computation’s physical cost and the choices that remain while adaptation is still possible.