Thirst sensation is the early symptom of dehydration that arises from a lack of fluids and/or increase in the content of certain osmolites such as salt in our body.

In most people dehydration symptoms become noticeable after 2% loss of one’s normal water volume and in addition to thirst may include dry skin, abnormally dark urine, tiredness and headache. 10% to 15% loss of water may result in dim vision, muscle cramps, dizziness. Water losses that exceed 15% are usually fatal.

In adults over age of 50, the thirst sensation diminishes. In a study elderly people were withheld from drinking water for 24 hours, and when in 24 hours water was made available to them, they still did not recognize that they were thirsty.

Water is the most important nutrient for our body, required among many things for digestion. It forms 50-60% of body weight, but exact amount depends age and sex: men have about 60%, and women 52% of body weight (because women have more body fat).

One of the signs of dehydration that everyone can see is the colour of urine: yellow urine indicates the beginning of dehydration, orange urine is the sign of true dehydration, and colourless urine says that your body gets enough water.

In temperate climates an average person's body loses about 2,5 liters of water a day through lungs (water vapor), sweating and urination. Daily water intake depends on many factors, but studies show that for active persons and people living in hotter climates it should be approximately 4,5 to 6 liters a day.

The main sources of water for the body are the food and fluid we consume. However, it also comes through normal metabolism as a by-product from the breakdown of food substances. For instance, 1 gram of carbohydrate produces 0.60 grams of water. Scientists believe that we should not wait until we get thirsty (because thirst is already the sign of dehydration), but drink water throughout the day.