Water is essential for daily functioning and health, and we can only survive a few days without it. Yet we are constantly losing water through sweat, urination, and even evaporation when we breathe.

This is why we have evolved a way to regulate and maintain water in our body. As with other animals, our survival relies on a strong biological drive to find and drink water to balance out fluid loss.

This is thirst – a dry feeling in the mouth signaling that we need to have a drink. This basic physiological mechanism is controlled primarily by part of the brain’s “control center” called the hypothalamus. The hypothalamus receives signals from various areas of the body and, in return, releases hormones that act as a messenger to signal the feeling of thirst.

What is dehydration?

Staying hydrated (having enough water in our body) is important for several reasonsincluding:

• regulate body temperature through sweat and breathing
• lubricate joints and eyes
• prevent infections
• digest and absorb nutrients
• eliminate waste (via the kidneys)
• prevent constipation
• brain function (including memory and concentration)
• mood and energy levels
• physical performance and recovery after exercise
• skin health.

Dehydration occurs when our bodies don’t have enough water. Even slight drops in fluid levels have notable consequencessuch as headaches, feeling dizzy, lethargy and difficulty concentrating.

Chronic dehydration may pose more serious health risks, including urinary tract infections, constipation, and kidney stones.

What does the evidence say?

Although thirst is one of the most fundamental biological factors in proper hydration, science suggests that our feeling of thirst and resulting fluid intake does not always correlate with hydration levels.

For example, a recent study explored the impact of thirst on fluid intake and hydration status. Participants attended a laboratory in the morning and then later in the afternoon to provide markers of hydration status (such as urine, blood samples, and body weight). The relationship between morning thirst levels and afternoon hydration status was negligible.

Additionally, thirst can be driven by environmental factors, such as access to water. For example, a study examined whether sufficient access to water in a laboratory influenced the amount of alcohol people drank and how hydrated they were. The relationship between their thirst and hydration levels was weak, suggesting that water availability influenced their fluid intake more than thirst.

Exercise can also change our thirst mechanismalthough studies are limited at this stage.

Interestingly, research shows that women feel thirst more strongly than men, regardless of their hydration status. To understand gender differences in thirstResearchers infused fluids into men and women, then measured their thirst and hydration levels. They found that women generally reported thirst with a lower level of fluid loss. It has also been found that women respond more to be thirsty by drinking more water.

Other ways to know if you should drink water

While recognizing that some people will need to drink more or less, e.g. a lot of peopleEight cups (or two liters) per day is a good amount of water to aim for.

But beyond thirst, there are many other ways to know if you need to drink more water.

1. color of urine: Pale yellow urine usually indicates good hydration, while darker, concentrated urine suggests dehydration

2. frequency of going to the toilet: urinate regularly (about four to six times a day) indicates good hydration. Infrequent urination may signal dehydration

3. skin turgor test: gently pinch the skin (for example, on the back of the hand) and observing how quickly the skin returns to its normal position can help assess hydration. Slow return may indicate dehydration

4. mouth and lips: a dry mouth or chapped lips can be early signs of dehydration

5. headaches and fatigue: frequent headaches, dizziness, or unexplained fatigue may be signs of insufficient hydration

6. sweating: In physically active people, monitoring the amount of sweating during activity can help estimate fluid loss and hydration needs. Higher sweating levels can predispose a person to dehydration if they are unable to replace the fluid lost when drinking water.

These indicators, used together, allow you to have a more complete vision of hydration without depending solely on the sensation of thirst.

Of course, if you’re thirsty, it’s always a good idea to drink water.