Excess alcohol consumption can cause dehydration in a variety of ways. Firstly, alcohol decreases the body's production of anti-diuretic hormone, which is used by the body to reabsorb water. With less anti-diuretic hormone available, your body loses more fluid than normal through increased urination.
Similarly, can you hydrate with coffee?
Juices and sports drinks are also hydrating -- you can lower the sugar content by diluting them with water. Coffee and tea also count in your tally. Many used to believe that they were dehydrating, but that myth has been debunked. The diuretic effect does not offset hydration.
Can you survive on beer?
During the 46-day feat, J. Wilson consumed only beer and water, emulating a centuries-old tradition once practiced by the Paulaner monks of Munich, Germany. How long could a man survive on beer and water? Not more than a few months, probably. That's when the worst effects of scurvy and protein deficiency would kick in.