Abstract: An in-depth understanding of the hydration mechanism of tricalcium silicate is an important basis for optimizing cement strength development. In this study, the adsorption of water molecules onto the M3-C₃S(001) surface at different water coverage levels (θ = 1/5, 2/5, 3/5, 4/5, and 1) was investigated using first-principles calculations. The results demonstrate that the conclusions obtained for single water molecule adsorption cannot be fully applied to multiple water molecule adsorption. The total adsorption energies become more negative with increasing water coverage, while the average adsorption energy of each water molecule becomes more positive with increasing water coverage. The water–water interactions reduce the water–surface interactions and are responsible for the anticooperative adsorption of multiple water molecules onto M3-C₃S(001). The formation of Ca–OH (–Ca) bonds favors the detachment of Ca from covalent oxygen, which reveals the significant role of dissociative adsorption. This work aims to extend the water adsorption study on M3-C₃S(001) from single water molecule adsorption to multiple water molecule adsorption, providing more detailed insights into the initial water reaction on the C₃S surface.