The involutive restriction of the renal, pulmonary, endocrine and buffer mechanisms also diminished the range of efficacy and possibility for adaptation of the water-- and electrolyte metabolism of old people. Under geriatric aspects many causes for the endangering of the water-- and electrolyte metabolism and the therapeutic consequiences are discussed. It is founded that in old patients the quicker metabolism imbalance means a stronger threat of life that the disease itself. Often the consideration of this problem in much cases of diseases can save the life of the old patient.