Water is essential for the formation of granites, but its origin and role in granite generation (i.e., dehydration vs. water‐fluxed melting) remain uncertain. These issues are addressed by combining water abundances and other geochemical indices in zircons from Late Mesozoic granites generated during the destruction of the North China Craton (NCC). The water contents in zircons from the NCC Early Cretaceous granites (763 ppm, median) are much higher than those of the NCC Jurassic granites (424–513 ppm), upper mantle and continental arc magmas (92–477 ppm). More importantly, the higher water contents in the voluminous Early Cretaceous granites also have higher zircon saturation temperatures, εHf(t), and lower δ18O values. These observations suggest a predominantly mantle origin for the water, and water‐fluxed crustal melting, in which larger water ingression produced more voluminous melts. The high‐water flux was likely related to the subduction of the Paleo‐Pacific Plate, which ultimately destabilized the NCC. Plain Language Summary The fact that water is essential in generating granites has been known for a long time. However, its detailed role is poorly understood due to heterogeneous source and complex melting reactions involved in the generation of granites. As a fundamental issue of granite genesis, it remains a long‐standing problem to distinguish the two major mechanisms, that is, hydrous‐mineral‐dehydration melting versus external‐water‐added melting. In this study, the water content of zircon combined with other lines of clues of I‐type granites that generated during the destruction of North China Craton (NCC) in Late Mesozoic collectively points to water‐added crustal melting rather than dehydration melting. The isotope composition of zircon suggests a mantle provenance of water. The highest water contents occurred in the Early Cretaceous granites, corresponding to the climax of the NCC destruction. Higher zircon water contents in Early Cretaceous granites indicate higher water‐flux into thelithospheric mantle and overlying crust by the subduction of the paleo‐Pacific plate. Accordingly, water played a significant role in cratonic destruction. Key Points Water contents of zircons from North China Craton Jurassic granites are comparable with continental arc magmas Higher zircon water contents are found in voluminous Early Cretaceous granites generated during the climax of cratonic destruction Early Cretaceous granites were generated by water‐fluxed crustal melting, the water in which has a predominant mantle origin