Water confined within the nano-to microscale pores of cementitious materials plays a crucial role in damage processes affecting the sustainability of cement pastes, especially for the binding material comprising calcium-silicate-hydrates (C-S-H).Here, we employed a combination of molecular simulation techniques (Monte Carlo and Molecular Dynamics) to investigate physical properties of confined water in open nanopores (connected with the environment) and closed nanopores (isolated from the environment) formed between C-S-H particles constituting the cement microstructure.