Management of abnormalities in water homeostasis is frequently challenging. Because age-related changes and chronic diseases are often associated with impairment of water metabolism in elderly patients, it is absolutely essential for clinicians to be aware of the pathophysiology of hyponatremia and hypernatremia in the elderly. The sensation of thirst, renal function, concentrating abilities and hormonal modulators of salt and water balance are often impaired in the elderly, which makes such patients highly susceptible to morbid and iatrogenic events involving salt and water. Clinicians should use a systematic approach in evaluating water and sodium problems, utilizing a comprehensive history and physical examination, and a few directed laboratory tests to make the clinical diagnosis. Furthermore, clinicians should have a clear appreciation of the roles that iatrogenic interventions and lapses in nutrition and nursing care frequently play in upsetting the homeostatic balance in elderly patients, particularly those who are in longterm institutional and inpatient settings.