During the Civil War (1936–1939), Spain became a testing ground of military technologies and tactics that were applied during World War II on a much larger scale. Due to artillery bombardment and aerial bombing, Madrid’s urban water supply approached the brink of collapse. The efforts of the workers of the state water company were fundamental to control leaks and guarantee the city’s water supply. In Barcelona, anarcho-syndicalists collectivized the private water supply company, and despite air raids expanded its services and carried out reforms that enhanced efficient management while achieving greater equity in the provision of water. The importance of water supply services in both cities shows the critical role of utility workers to urban resilience in cities at war.