European ammunition expansion is usually measured through new filling lines, propellant and explosive capacity, shell bodies, contracts and public production subsidies. That perspective captures the assets that make defence products, but not all the industrial systems that determine whether those assets can run continuously. Plants that make propellants and explosives draw water for processes and cooling, and they must treat and discharge their effluent within the conditions of their permits. A production line can therefore be financed, built and staffed and still be unable to run at its intended rate if the water it needs cannot lawfully be taken, if its cooling cannot absorb the additional heat, or if its wastewater cannot be treated to the standard its permit requires. The relevant question for European rearmament is narrower than whether the continent has enough water in aggregate. It is whether individual production sites possess legally authorised, technically adequate and continuously available water services that remain compatible with higher production rates, and whether the public record allows that to be known. Answering it requires treating water infrastructure as an operating system whose permitting, financing, ownership, maintenance and environmental performance can follow a different critical path from the production equipment it supports.