«Water is not so good. I once drank it. It does not slake thirst.» These are the words of an old drunkard Omar. You should not be serious about it, because the poet used this hyperbole to express his love for wine. Of course, he drank water.
Alcohol dehydrates the body tissues. When you have hangover, water shortage is about 2-3 liters. That is why it is recommended during the first 2 hours after waking up to drink 1.5 liters of liquid and continue to drink it throughout a day as much as possible. In such way it is possible not only to compensate the lack of water, but also to get rid of toxic products in your body formed by the decay of alcohol. People with high blood pressure (especially lower, so-called diastolic) should be careful in drinking water. Excessive fluid intake can cause high blood pressure.