Alterations of water homeostasis in the elderly, e.g. diminished renal function, alterations in regulation of thirst and in secretion of hormones maintaining water and electrolyte balance, as well as changes in body composition, result in the decreased ability to maintain water balance. As result of these multiple changes, the elderly have more frequently dehydration and hyponatremia. The normal hydration status is essential for normal functioning . Today there is still the lack of internationl consensus on the definition and management of hydration status. Health care professionals should pay more attention on the possible alteration of water and electrolyte balance in the elderly.