The Black Bedouin Goats (BBG) inhabit the arid and semi-arid areas of the Arabian and the Sinai peninsulas. In the desert the migrating herds cover long distances and are watered only once every three days. During migration the animals lose up to a third of their body weight, which they regain by ingesting water within minutes after arriving at a watering place. No water intoxication occurs despite large osmotic gradients, because most of the ingested water remains in the rumen for hours. For closer characterization of such water storage and movement, we carried out in-vitro investigations on the epithelia of the BBG´s forestomach. Zannen Goats (ZG) were taken as a control group. A modified Ussing-chamber technique was used for direct measurement of water flux. Iso-osmotically, the rumen showed only very small rates of water flux as high as 0.04 - 0.06 µl · cm-2 · min-1. The flux rose clearly and proprotionally to the osmotic gradient in both hydrated and dehydrated animals up to 0.29 - 0.58 µl · cm-2 · min-1 at an osmotic gradient of 200 mosmol · kg-1, mucosal < serosal. The values of the dehydrated epithelia were significantly lower than those of the same individuals in a state of hydration. The omasum was characterized by a high iso-osmotic flux of 0.11 - 0.16 µl · cm-2 · min-1, which rose proportionally to the osmotic gradient up to 0,35 - 0,43 µl · cm-2 · min-1. The abomasum showed no iso-osmotic flux and only very small values at high osmotic gradients. Mannitol containing buffers (mucosal) resulted in significantly lower fluxes compaired to those of the same osmotic gradient without mannitol, thus indicating an ion-depending fraction of water flux. These results demonstrate that the BBG are "rumen drinkers" whose extraordinarily dense rumen epithelium enables water storage. This effectively protects the goats from water intoxication and guarantees their survival in the desert.