They say that beer and coffee are diuretics and will make you pee more fluid out than you take in by drinking the coffee/beer.
Now being the scientific type I simply follow where the data takes me. So I opine that this can not be true of coffee and beer. If it were true I would be a dessicated husk by now with bits flaking off and blowing away in the breeze by now.
Don'cha just love science?