In a world where the effects of climate change on weather patterns is accepted as real and serious, the problem of decreasing the production of carbon dioxide is perceived as increasingly important. The cement industry produces 5-7% of the world's carbon dioxide emission and its survival will depend on improvements in the production of concrete which will be both more durable and require less carbon dioxide per unit of manufacture than the currently produced concrete. The durability of concrete is related to its ability to limit fluid transmission and knowledge of how to reduce the rate at which water will be transmitted through cement paste is critical to improving durability. However, because of the complex chemical and physical nature of cement pastes, understanding water mobility is a great challenge. Many techniques are not applicable simply because they are not sensitive to the range of size from angstroms to microns and the extent of water interaction with the cement where water can either be chemically bound at hydroxyls or physically free in large pores. In this review paper, we present the most up to date results on the physical chemistry of the water/ cement paste interactions studied by quasi-elastic neutron scattering. These results bring new insight to the mobility of water in the gel pores, the small pores (radius less than 50Å) that control the rate of water transmission in the cement pastes from which high quality concrete will be made.