Human hydration

Find out all the information about human hydration you may need: from the importance and benefits of a healthy hydration and the consequences of dehydration, to the hydration needs according to age, special populations and special conditions, and the sources of water which contribute to fulfilling your needs.



Appropriate hydration of the body is an absolute requirement for health and is essential for life itself. Water sustains the body’s many vital chemical reactions and maintains correct body functions.

Water plays many important roles within the body. Water is the major part of most of the body’s cells (except for fat cells) and it also cushions and lubricates the brain and the joints.


Dehydration is the loss of water from the body in excess of the amount consumed.

Dehydration occurs when the body loses more water than is taken in. It is often accompanied by disturbances in the body’s mineral salt or electrolyte balance – especially disturbances in the concentrations of sodium and potassium.


It is often said that thirst should be the guide for drinking, but what does it mean to be thirsty?

Many people talk about this sensation, but few people can say that they actually feel it. Many authors have studied the physiological regulation of thirst, fluid intake and body fluids (1-6). Here we show you the physiology of the thirst mechanism making the body looking for liquid.


Humans can, by conscious effort, over-ride many of the signals that drive the regulatory processes involved in water balance

Thirst tells us that we should drink, but we can choose not to do so. Likewise, we can drink when not at all thirsty, as when offered drinks in a social situation where it might cause offence to refuse.

Hydration and Diet

A total diet approach to healthy hydration

Optimal physical and cognitive performance depends on us maintaining healthy hydration levels. This is why hydration is of interest to individuals as well as to public health experts.

4 key moments in Hydration

Studying, driving, performing physical activity and at work.

Any moment is good to take hydration into account, but here we propose four particular times when hydration needs should be specially considered: when studying, when driving, when performing physical activity and at work.

Nutrition & Beverages

Total daily water intake is the sum of water content coming from all types of beverages and foods.

Replacement of the body’s water and salt losses is essential to maintain appropriate hydration and a good health status. Replacement of water can be achieved through food and beverages. It is calculated that of the total water consumed, 20-30% typically comes from food and 70-80%

Hydration levels

Water needs vary between individuals and according to diet, environmental conditions, activity levels and a range of other factors.

Reference values for total water intake as a guide to achieve appropriate hydration levels are given for different groups of ages as well as for special conditions such as pregnancy or lactation. Some hints and tips about healthy hydration are also offered.

Assessing Hydration Status

Why measure hydration?

There are different reasons for assessing hydration status, and the method of choice will depend on the population of interest, the level of precision required, on the facilities and expertise available, and on budgetary constraints.

People with different needs

Some age groups are especially sensitive to the effects of dehydration; some people also have special hydration needs due to particular conditions. This is the case for children and elderly people and for women during pregnancy and lactation.

Climate and Environment

People live, work and exercise in different environments and climatic conditions, all of which can influence daily fluid losses and water requirements.