Vital: drinking water
The body mainly obtains its elixir of life – water – through drinking. Its liquid intake also comes from solid food and metabolic water. For men, water makes up 50 per cent of total body weight. For women the proportion is somewhat higher, at 60 per cent. Water takes on a variety of important functions in the body, e.g. as a means of transportation and dissolver of nutrients, as a component of cells or as a reactant in biochemical processes, to name but a few. The body is constantly excreting liquid via the kidneys, intestine, skin and respiration, which is why taking in lots of liquid across the whole day is so important. If it has insufficient liquid, the body regulates this need via the sensation of thirst.
How water requirements change over time
A healthy adult will experience thirst if his or her body has lost over 0.5 per cent of its weight in the form of water. However, this does not remain constant as we grow older. The key changes that come about with ageing and affect diet and nutritional status are related to bodily composition, including weight, energy and nutrient requirements, and the sensation of thirst.