Tidally locking a rock or metal moon isn't too hard and the understanding of how a solid moon behaves while tidally locked is relatively well understood. However, can a water moon be tidally locked or would the movement of the water prevent locking?
I don't have any specific parameters for size or orbital distance in mind, just an existence proof ($\exists$) that a tidally locked moon made of water is possible. The surface of the moon should be liquid and as far down as H2O can stay in a liquid phase. Whether it has an ice core or iron/stone core doesn't matter to this question.