Abstract: Optional function of body systems depends upon fluid and electrolyte balance; however, across the lifespan, disorders of fluid and electrolytes offset this, and the causative factors are varied. Nurses play a major role in the management of fluid and electrolyte balance. This article focuses on the role total body water content, plasma proteins, kidney function, and drug metabolism have on the age-related physiology impacting fluid and electrolyte balance, and on nursing implications.