Although most common forms of alcohol that we drink are already diluted with water, we should always aim to keep ourself hydrated when drinking alcohol. Alcohol can be very dehydrating and we should keep well hydrated.
And when drinking alcohol you should try to stick to the recommended guidelines for men and women. This can be commonly found on the containers themselves as well as the national websites.
However, do not drink too much water at once as it can unbalance your salt or sodium levels leading to various problems.