Chemical changes in the kidneys
The increased amount of fluid in the body from alcoholic beverages
The frequent urination issues that alcohol causes are primarily due to chemical changes that occur when drinking alcohol. Alcohol suppresses areas of the brain that release a chemical called vasopressin. In normal conditions, this chemical causes the kidneys to reabsorb some of the fluid that is filtered through the kidneys.
This effect helps to regulate the amount of urine produced. When the amount of vasopressin in the body is lowered, the body does not reabsorb as much fluid from the kidneys, causing the kidneys to increase the amount of urine produced.
In addition to the effects of alcohol on vasopressin, the volume of alcohol also contributes to the amount of urine produced. While the effects of vasopressin on the kidneys have the greatest effect on urine production, the amount of alcohol consumed also increases urine production, as the body must get rid of that extra fluid. Essentially, the more a person drinks, the more frequently they will have to urinate.
Hence because of alcohol, less ADH produced= Walls of DCT and collecting duct less permeable to water= Less reabsorbed into the blood= More excreted as urine.