Supported lipid bilayers (SLBs) are a very popular system for the study of biomimetic membranes. Understanding of the interactions between the solid substrate and the lipid membrane opens pathways to the design of new materials with fine-tunable properties. While it is possible to study SLBs via molecular dynamics (MD) simulations, difficulties still remain for these strategies; in particular, the confined water layer thickness and structure are difficult to reproduce in simulations. We have explored different coarse-grained (CG) models for the membrane/support interaction, and their impact on the substrate hydration level. Our results highlight the relevance of including long-range interactions in CG-MD simulations of fluid SLBs. Modeled neutron reflectivity curves are deduced from the structures obtained by molecular simulations, and substrate parameters are optimized to match the experimental and modeled reflectivity curves. We expect our coarse-grained approach to open new perspectives for the simulations of SLBs of increasing complexity, including lipid layers of complex compositions, or adsorbed lipidic layers on patterned surfaces.