From November 1979 to May 1982, I had the "honor" of serving time at Evin political prison, Teheran Iran. Evin is the historical prison which has set the pace of revolution in the country. At Evin it was discovered that increased regular intake of water improved the clinical picture of peptic ulcer disease. One of the main components of this picture was pain of varying severity, sometimes very severe indeed. Theoretical research to find the physiological reasons for the observed effect of water, in a condition currently classified as disease, has revealed a neurotransmitter, an osmoregulator, a water intake promoter status and a role for histamine. The action of histamine seems to be coupled to the efficient function of the cation pumps. Histamine and serotonin are involved in the regulation of the body's water balance. Cellular "free water" insufficiency produces a disturbance of tryptophan metabolism; it is this disturbance and induced functional deficiency altering the homeostatic balance that produces pain and eventually tissue transformation and/or damage. This pain is being introduced as a signal system denoting free water deficiency of the cell and, therefore, it should be classified as thirst pain. Histamine and the reninangiotensin system also coordinate the water intake and sodium balance of the body. With the induction of renin-angiotensin system for increase in water intake, threshold rates for water intake and the threshold rates for raising blood pressure seem close.