Mixing ionic liquids (ILs) with water proposes an effective way of designing IL solutions with engineered properties that have applications in various processes/industries. Understanding molecular interactions of ILs, water, and carbon dioxide (CO2) is of great importance in the selection of ILs with high selectivity and solubility for CO2 capture application. We perform molecular dynamics simulations to investigate the effects of water concentration on excess energy, molecular distribution, and dynamic behaviors of mixtures of 1-butyl-3-methyl-imidazolium acetate ([Bmirn][Ac]), water (W), and CO2 at different water concentrations. The results of this study include radial distribution functions, coordination numbers, water cluster size distribution, hydrogen bonding, and diffusivity coefficients in IL/W and CO2/IL/W systems, using [Bmim] [Ac] as the IL, at various process conditions. Analysis of the water clusters in the IL/W system reveals that the water clusters are connected mainly through hydrogen bonds. The presence of water in the IL solutions increases the diffusivity of cations, anions, water, and CO2 molecules in the mixture because of the reduced viscosity of the solution and the hydrophilicity of [Bmim] [Ac]. This study highlights the effect of water (as an additive to IL) on key parameters such as diffusion coefficient and cluster formation in optimal design and operation of carbon capture processes.