Well, it doesn't matter whether it's beer, wine, or triple malt scotch. They all contain alcohol, and that's what is causing the dehydration. Alcohol is a diuretic, which means it will dehydrate you. Regardless of how much water is in that beer, it can't keep up with the alcohol. The only way to avoid dehydraton is to drink enough water along with the beer to conteract the alcohol's effect.

Alcohol is poisonous above a certain dosage--all substances are poisonous at some dosage, including water--and the body wants to get rid of it by dissolving it in enough water to carry it away to the kidneys, the sweat glands, the lungs, and the liver where it is changed to something else and eliminated. Except for an extremely low-alcohol near-beer, even ordinary 3.2% beer doesn't have quite enough water to take all the alcohol away, so you're thirsty the next morning. Except for no-alcohol near-beers, I doubt that any near-beer would have such a low percentage, besides which nobody considers drinking a glass of water in the morning to be a problem requiring a special formula. Can you imagine an ad campaign for "The Only Beer that Doesn't Make You Want to Drink Water"? For that matter, sea water is also made primarily of water. So why does it dehydrate you? Because salt, like alcohol, needs to be escorted out of the body by a large amount of water.

Alcohol inhibits the release of ADH (antidiruetic hormone) by the adenohypothesis (aka the anterior pituitary). ADH normally targets the kidneys, which respond by absorbing water back into the body. Without ADH, you urinate more contributing to dehydration.

1) Because the 5% of alcohol in beer will lead your body to lose more water through urination than the 95% water of your intake. So if you drink beer, even before the ingested water could start to have a positive rehydration effect, the ingested alcohol will provoke a further dehydration effect. Note that non-alcoholic beer does not dehydrate you (but this might not be the case for low-alcohol beer). 2) "Dehydration Alcohol is diuretic. This means it encourages the body to lose more water than it takes on by halting the production of the body's anti-diuretic hormone, resulting in you needing to go to the toilet excessively and so speeding up the loss of fluid from your body, leading to dehydration. Alcohol also attacks our stores of vitamins and minerals, which need to be in the correct balance for the body to function normally. Dehydration caused by drinking can affect the balance by draining potassium from the body, resulting in thirst, muscle cramps, dizziness and faintness." Source and further information: http://www.alcohol.org.nz/BodyEffect.aspx?PostingID=671 3) "Dehydration Alcohol has been known to mitigate the production of the ADH (antidiuretic hormone), which is a hormone that acts on the kidney, favoring water reabsorption in the kidneys during filtration. This occurs because alcohol confuses osmoreceptors in the hypothalamus, which relay osmotic pressure information to the posterior pituitary, the site of ADH release. Alcohol makes the osmoreceptors signal as if there was a too low osmotic pressure in the blood, which triggers an inhibition of ADH. Consequently, one's kidneys are no longer able to reabsorb as much water as they should be absorbing, leading to creation of excessive volumes of urine and subsequently overall dehydration." Source and further information: http://en.wikipedia.org/wiki/Short-term_effects_of_alcohol#Dehydration 4) Further information: http://www.symptomsofdehydration.com/alcohol-dehydration.htm http://www.nt.gov.au/health/healthdev/aodp/lwap/playhard.shtml

Roger Kovaciny is a practical guy he speaks of poison. Pre-poison is usually spoken of as intoxication among the toxicology set so it could be applied to caffeine as well. Both are metabolized in the liver and flushed by the kidneys. When discussing hydration, the kidneys are the organ most frequently considered but the skin is sometimes the biggest player (http://www.bikeforums.net/archive/index.php/t-330004.html ) and lungs are not far behind. Personal experiences of often getting well past the first pitcher without peeing and at times peeing with the first sip, say the internal controls others speak of, like they know, are always working a compromise: Can I give up water (dehydrate from where I am) to purge the caffeine and alcohol or would that state of dehydration be worst? Without further purging the liver is on its own to clear the intoxication, those accumulated (not purged) liver wastes lead to hangover and weight gain as well as thirst. Peeing purges intoxicants until the state of dehydration prevents the purging; the Creator thought of everything. It works just as well for salt and vitamin C.