Muscles atrophy with age, and seniors consequently have less water in the body than younger adults. From infancy to our elderly years, the composition of the body changes from 75% to 50% water on average. The kidneys’ ability to reabsorb water decreases with age, so water is lost from the body in greater amounts.
Seniors have the same water needs as younger adults, even though their sensation of thirst diminishes as they grow older; they need to monitor water intake carefully to avoid dehydration6. Elderly people feel less hungry, and eating less food means the body is missing a source of hydration. Older people are also at higher risk of illness and serious injury and adequate water intake is vital to prevent hydration resulting from fever and vomiting/diarrhea as well as blood loss and wound secretion.
Sources: (6) Jéquier et al. Water as an essential nutrient: the physiological basis of hydration. EJCN 2010, 64: 115-23