Hope this helps to answer your question.....
Contrary to what many people believe, drinking water does not cause fluid retention. In fact, drinking more water, not less, can actually help to correct the problem. However, drinking alcohol can cause you to retain water. But unless you chronically abuse alcohol, water weight gain is usually only temporary. Unfortunately, alcoholism can lead to impaired liver function, which causes excess fluid to build up in the feet, ankles and legs.Dehydration
Drinking too much alcohol can lead to dehydration, and therefore, problems with water retention. People who drink heavily often need to urinate more frequently or may perspire more than usual. They also tend to drink less water and fewer other fluids. Urination and sweating both increase the amount of fluid your body loses, especially if you don't replace the fluids. When the body is dehydrated, it tends to retain water to make up for the loss. A major health concern is that when you don't keep your body well hydrated with fluids, the organs have to work harder.
In answer to your other post, the OP & I were only suggesting/advising you not to weigh mid week as you wont get a true reflection of your weight & if you hadn't jumped on the scales you wouldn't have seen the 2lb gain lol!.....but appreciate your good question about water retention