The ultimate guide to water, thirst and staying hydrated

The need for water and staying hydrated has instrumental in the growth of every civilization. In Homer poems people take cold water showers for hygiene and warm water showers for therapeutic purposes and to recover from exercise. Thales defined water as the basic element for life. Aristotle, confirmed this while talking about the classical elements. Hippocrates wrote that water influences people’s personalities.

Without water, life would never have appeared nor survived.

Water in the human body

About 60% of the human body weight consists of water. The Cerebrospinal fluid and liquid bone marrow (99%), blood plasma (85%), and the brain (75%) are the areas with highest density of water.  The proportion of water in our body changes with age: a fertilized egg has 90% water, an embryo is 85% water, 74% of a baby’s total weight is water; an adult is 55-60% water, and in an elderly person reduces to 51% in men and 45% in women.

Water is involved in most of the body functions and water homeostasis is basic for the hydroelectrolyte balance, acid-base balance, thermal balance, and other metabolic processes. A 2% reduction of water can affect thermoregulation and plasmatic volume. A 7% reduction can cause hallucinations, a 10% dehydration can lead you to death.

Scary? We lose large amounts of water through urination (0.05oz/day), stool (3.3oz/day) and sweating (30.4oz/day). This loss has to be restored with our diet.

Water regulation in the body

Since we lose water in our daily activities, all animals have developed amazing mechanisms to maintain and replenish water and body fluids. For these mechanisms to work well, the coordination between sensitive detectors all over the body have to be perfect. They are connected to brain integration centers that process all the information. These centers are also sensitive to humoral factors (neurohormones) that occur to adjust urination, natriuresis (amount of sodium in urine), and blood pressure. The brain processes all these information and controls the organs related with water regulation such as kidneys, sweat and salivary glands, and also creates thirst to stimulate water consumption.

The image below explains this well. The brain notices any changes in the osmotic pressure (related to sodium) or the arterial volume (related to the quantity of water we have) and reacts by adjusting fluid intake or increasing/decreasing urine.

Hydration vasopressure
hydrated thirst regulation mechanism

Diving deeper into the regulation mechanism

As we have been saying, ⅔ of water inside our bodies occupies the intracellular space and the other ⅓ occupies the extracellular space.

hydrated body water compartments

When we suffer from a water deficit, an ionic concentration is produced in the extracellular space attracting water from inside the cell causes a size reduction. Brain sensors notice this shrinkage and controls the water consumption and urine excretion.

When our body has too much water, the inverse occurs. The ionic concentration is reduced to allow the body fluids to carry more water inside the cell. Thirst disappears, and the kidneys excrete more water.

Thirst regulation in the body

Now that we know the importance  of hydric and osmotic balance in the intra-extracellular space, it’s easy to understand that we have two kinds of physiological thirsts.

If water loss exceeds salt loss (ex: when we have a bad diet or urination increases) the ionic concentration increases. As a result of this, water from the intracellular space goes to the extracellular space. At the same time, the body uses this as a main regulation mechanism to release the antidiuretic hormone which stops urination and gives us a the feeling of thirst.

On the other hand, when we lose more salt than water (sweating or poor water consumption) the hyponatremia occurs and the water goes to the intracellular space and the cell size increases. This way the lack of water will generate some issues in the liquid accumulation in the extracellular space and the hyponatremia will generate a cell size increase.

Our body reacts to this liberating hormone called Angiotensin II which generates vasoconstriction (constriction of blood vessels), causes thirst, and induces the release of aldosterone in the adrenal cortex. This hormone facilitates renal retention of sodium and salt appetite. Once the sodium levels are regulated, the extracellular space takes the water back and the body returns to a homeostatic state.

In general, most of the daily situations, the sodium and water that we lose is proportional between them so the tonicity will be stable. This kind of dehydration is known as isotonic dehydration and happens in 80% of the dehydration cases according to this studyThis is the reason that in most of the cases of dehydration we have to think how to recover water and minerals. 

What should we drink?

Yes, that one was easy to guess. Water.

But it’s a tricky answer. We mean real water, the one we have been drinking all our history. If we pee the same amount of water we consume, it’s still possible that we are not hydrating properly. When we drink water low in minerals, (distilled water being the extreme) we will take water to the intracellular space inflating them like balloons and activating the diuresis in an useless attempt to get back an osmotic balance again.

Humans have drank water all throughout history. So our body expects mineral water. In this perspective, drinking low mineral water makes no sense: we will pee more and will recover the minerals we need. Our body will generate arterial vasoconstriction and increase the arterial pressure.

How and when should to drink water. Let your thirst guide you

Thirst is a good indicator for most of the people. If you are thirsty, drink!  If you are not, don’t. In fact, a lot of people believe that thirst is an indicator of being dehydrated, but this has never been proven as we can see in this study.

Why some people never feel thirsty?

One of the most common problems that my patients have is that they have lost the capability to feel thirst. It’s hard to understand how the body system can not notice the lack of a precious element such as water. One of the most accepted hypothesis is that thirst loss is related to they way we drink water nowadays.

As soon as we drink water, some specialized detectors in our throat inform the brain that we have ingested water. This sign persuades us to reduce the antidiuretic hormone and indicate that we’re not thirsty. This happens even before the water we drank brings an osmotic balance. Now, if you look at our history, it has never been as easy to get water as it is now. Even a few years ago we had to walk to a fountain and drink till we didn’t feel thirsty anymore. Today, we take a bottle of water, drink a couple of sips, and the thirst is gone. We don’t feel it’s necessary to drink more since we always have access to water.

Add to it the fact that the water we are drinking is semi distilled. It’s highly probable that we don’t feel thirsty and at the same time we are not hydrating ourselves well. For this reason, our main source of liquid should be mineral water. Also a regular diet which includes fruits and vegetables. Even better if they are water and electrolytes rich. 

Thirst is not enough as a method to request for water. Athletes, for example, do high intensity physical activity that require them to control the amount of water and sodium they consume. This also applies to people who have health issues that affect the thirst sensation such as diabetes and kidney diseases. These people need another kind of measurement for their daily needs. When a thirst sensation is felt for several days, this can be a symptom of hyperglycemia or other diseases, and not necessarily a sign of dehydration.

How do you know if you are hydrated?

  • Urine too light or too dark

When urine is too light, it indicates that the body is trying to throw water to have a balance between the intracellular and extracellular space. This would be a good moment to drink hypertonic waters. On the other hand, if urine is too dark as we can see in the picture, maybe we need more liquid.


  • You pee immediately after drinking water

Check the water you are drinking (it’s probably low mineral water). Add fruits and vegetables to your diet, and try not to drink in sips. It’s better to drink in bigger quantities and make this a habit.

  • You are panting

One of the reasons you are trying to catch your breath is the lack of sodium in the extracellular space. Due to an osmolarity difference, the water is directed to the intracellular space and the cells swell.  Again, check the type of water you drink and ask yourself if you should consume hypertonic drinks.

  • You have Edema

If you have the most common kind of water retention. Water is being accumulated in the extracellular space. This happens for different reasons (toxemia, renal troubles, acidity), and it is probable that sodium levels are high. Check your urine and try to increase the amount of water you drink daily.

Conclusion: How to stay hydrated

  1. Eat fruits and vegetables. The ideal situation is adding a portion of vegetables in lunch and dinner and eating two fruits per day.
  2. Drink mineral water.
  3. Bring back the thirst sensation. If it is possible, do activities that make you sweat! It increases the levels of hormones related to thirst. Also, it is calculated that the osmotic pressure in blood change every 4 hours. So it will be better if you drink when you wake up (let’s say at 6), and then drink every four hours (10, 14, 18, 22).
  4. Bone broth has to be included in your weekly diet, it is a great source of liquid and minerals.
  5. Go drink water now!

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