It’s not so much that the body is bad at reabsorbing water, rather it depends on the rate of metabolism of alcohol and the elimination of alcohol by-products from the body.
First of all, the ethanol content of alcoholic beverages is expressed by volume percent or by proof. Proof is a measure of the absolute ethanol content of distilled liquor, and is calculated by determining its specific gravity at an index temperature. In the United Kingdom, the Customs and Excise Act of 1952, declared proof spirits (100 proof) as those in which the weight of the spirits is 12/13 the weight of an equal volume of distilled water at 11 degrees C (51F). Thus, proof spirits are 48.24% ethanol by weight, or 57.06% by volume. Other spirits are designated over or underproof, with the percentage of variance noted. In the United States, a proof spirit (100 proof) is one containing 50% ethanol by volume
For a typical 70-kg person, a “standard drink” (15 g of ethanol),defined as 1 oz (30 mL) of 100 proof liquor, about a 4-oz (120-mL) glass of wine (12% ethanol), or about a 10-oz bottle (300-mL) of beer (5% ethanol), could raise blood ethanol concentration by 43 mg/dL (9.35 mmol/L). However, this is the theoretical maximum ethanol concentration, based on instantaneous and complete ethanol absorption and no distribution or metabolism following a “standard drink” by a typical 70-kg person.
Following complete distribution, ethanol is present in body tissues in a concentration proportional to that of the tissue water content. The concentration in the blood is maintained by back diffusion, which occurs whenever the concentration in the blood falls below that of the tissues.