When we talk about food, we hardly ever consider water, which is actually the most important food. Suffice it to say that without drinking, you can survive on average no more than three days, while without eating, you can survive, albeit with severe metabolic disorders, for more than a month.
Why do we need water so much? Because it is the largest percentage component of our body (in adults it adds up to 60-65% of body weight), and because we “lose water” continuously: first with urine, but also with the so-called “extra-renal loss” represented by sweat (this amount is very variable, depending on the outside temperature and the activity that is taking place), transpiration (ie the evaporation of water through our skin and mucous membranes), and feces.
How can we regain the water that we lose? We have both “endogenous” sources and “exogenous” sources of water. The endogenous sources refer to the water we produce during nutrient catabolism. This “endogenous water”, however, is not sufficient to cover our losses, and therefore we need to source water from the outside (“exogenous” water).
The most obvious source of water is of course water itself, but food counts too: not only drinks, which contain a very high percentage of water, but also other foods. The water content in food is variable, in general it is very high in fruit and vegetables but can also vary a lot among these too: the amount of water in an orange is much higher than in a banana!
Although the amount of water consumed with drinks and food may vary greatly depending on one’s diet, it is not enough on its own. Therefore, it is crucial to incorporate water itself as a drink in your diet. But how much? Of course, it depends on how much water is in the food we consume, but to be on the safe side it is important to drink 1-1.5 liters of water a day. But drinking this much water is not a commonly practiced habit, and actually most people are dehydrated.
There are two systems that try to maintain correct water levels in our bodies. The first is the production of an antidiuretic hormone which, as the word implies, reduces the volume of urine we emit and saves us water. The second is the thirst center, the nervous structure of our brain that makes us feel the sensation of thirst. But be careful: when we feel thirsty we are already dehydrated: we have to keep drinking even before we are thirsty.
But what happens when we get dehydrated? A loss of only 2% of the body’s water content leads to problems of thermoregulation and alteration of physical performance. With losses of 5% or more, cramps begin, and losses over 7% cause hallucinations and life-threatening risks. Even without reaching those levels, if we don’t drink much, our skin will be drier and we may have problems with constipation because our feces do not have enough water. And it is not true that drinking too much leads to water retention: water retention is caused by excess sodium, and drinking more water helps to resolve it.
And as a final tip, let’s remember that, proportionally, children need more water than adults: we must never send our children to school and to play sports without giving them a bottle of water.
Department of Agricultural and Food Sciences
University of Bologna