Adding a small amount of water to ionic liquids can greatly reduce the viscosities of ionic liquids, which is believed to be an effective and economical method to make ionic liquids being applied practically for carbon capture. However, how the water content influences the bubble behavior which is used to calculate transfer properties; this is important but has not been studied systematically. In this work, the rise and deformation of single CO2 bubbles in ionic liquids with different water contents were investigated using a high speed image pickup system. The results indicate that a small amount of water has a significant influence on the bubble behavior in ionic liquids. The viscosity plays a more important role in determining the bubble behavior than the surface tension. Two new empirical correlations verified by experimental data were proposed to predict bubble velocity and bubble diameter in different ionic liquid systems.