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How much water do we really need? How does hydration actually work? And what are the specific health benefits associated with maintaining proper hydration? As we embrace the summer season and brace ourselves for the soaring temperatures, it’s crucial to prioritize our well-being by taking necessary precautions. We’re all familiar with the concept of hydration, but there are still lingering questions that deserve attention. Join us as we embark on this exploration of the vital aspects of staying hydrated during the warm season.

We’re thrilled to dive into the captivating realm of hydration and its myriad connections to our overall well-being. If you’re eager to explore the links between hydration and mental health, as well as how staying hydrated affects cardiovascular risk and longevity, read those articles here.

Stay tuned as we uncover invaluable insights and discover the numerous benefits that proper hydration can bring to our lives.

How is hydration regulated in our bodies and on a cellular level?

Water is essential for life and all cells require water. Humans can survive without water only for days. Our bodies contain mostly water with about 55 % of body weight in the elderly and 75 % of body weight in infants (1). Water is important because it plays a crucial role in cellular homeostasis and life.

We, humans, just like animals, have developed a sophisticated system to regulate body water and fluid intake by thirst to avoid dehydration. Most of our drinking is triggered by the lack of water leading to a feeling of thirst and a physiological response known as regulatory drinking. In addition, there is non-regulatory drinking, which involves drinking for pleasure rather than quenching thirst. Examples of non-regulatory drinking include drinking coffee, tea, or alcoholic beverages. The kidneys play a crucial role in this process by efficiently eliminating excess water.

The mechanism behind water homeostasis (regulation) is complex as it aims to maintain the balance between constantly changing water and minerals in the body. These sophisticated mechanisms are so sensitive and precise that are activated with a deficit or excess of only a few hundred millilitres of water.

This process involves the coordination of detectors at different sites in the body, which are linked by neural pathways to integrative centers in the brain that process this information. These centers are also sensitive to different neurohormones. Instructions from the integrative centers are conveyed to the “executive organs” such as the kidney, sweat glands, and salivary glands, as well as to the part of the brain responsible for corrective actions such as drinking. These instructions are conveyed by certain nerves in addition to the neurohormones (1).


But how does this regulation work on a cellular level?

In our bodies we have water inside our cells (intracellular) and outside our cells (extracellular). When there is a water deficit, the space outside our cells becomes more concentrated increasing the ionic concentration of the extracellular space (1). That causes the water from inside the cells to move to outside the cells leading to cell shrinkage. This shrinkage is detected by two types of brain sensors, one controlling drinking and the other controlling the excretion of urine by sending a message to the kidneys mainly via the antidiuretic hormone vasopressin to produce a smaller volume of more concentrated urine (1). When there is an excess of water, the opposite processes occur, and more water reaches the cells, and ultimately the kidneys excrete more water.

The kidneys are thus crucial in maintaining fluid balance in the body. They work better when there is plenty of water available. When water is scarce, the kidneys produce concentrated urine, which requires more energy and puts more strain on the kidneys. This can happen when the kidneys are under stress due to a high salt or toxin intake. Therefore, it is important to drink enough water to keep the kidneys healthy (1).

Hydration goes beyond water.

When it comes to hydration, there are various sources available beyond just water, and it’s important to note that the composition of water itself can vary. Hydration can be also obtained from other beverages and food, and even to a small extent from the oxidation of micronutrients. Approximately 20% of our water intake is estimated to come from the food we consume, although this can vary depending on our diet choices (1). It is worth mentioning that although sugary beverages provide hydration, regular consumption of sugary beverages is associated with weight gain, obesity, type 2 diabetes, heart disease and others. Explore more about the sugar’s effect on aging here.

The water itself can also vary in composition. It can have different hardness or softness, it can come from spring or well, be carbonated or distilled all with different pH.  We are fortunate to have high quality tap water in Sweden and we rank among the highest in the world in terms of water quality (2), (3). The quality of tap water is often discussed due to the possibility to endocrine disruptors and mostly related to the amount of fluoride in water which if too high can lead thyroid disruption. Discover more about thyroid dysfunction causes and symptoms here.

While there is ongoing debate about which water is considered the “best” in terms of hardness, pH, and temperature for consumption, this article will not cover those specific details. However, if you’re interested in learning more about these aspects, there is a fantastic podcast available for free from Prof. Huberman’s laboratory that delves into these topics in depth (How to Optimize Your Water Quality & Intake for Health – Huberman Lab) . Prof. Huberman is a leading neuroscientist in the Stanford School of Medicine and his work has been published in top scientific journals and featured in Time, BBC and other media outlets.


How much do we need to consume to ensure proper hydration?

The optimal amount of fluids required for proper hydration can vary depending on several factors, including environmental conditions, temperature, humidity, and physical activity. In this discussion, we will specifically address recommended fluid intake levels during periods of rest. While there is ongoing debate surrounding the precise quantity of fluids needed, the Swedish Food Agency suggests a minimum daily water intake of 1.5 liters (2). These are general guidelines, and a personalized approach is always recommended.


Does it matter when we drink?

We wondered if the timing of drinking is important, and it turns out that it is. Research suggests that the time we drink water is related to our body’s internal clock (circadian rhythm) and our kidneys (4). Our kidneys are responsible for filtering fluids in our body and this process is strongly influenced by our internal clock. The genes that control our internal clock are expressed in every cell of our body, including the kidneys (4). These genes can impact whether our kidneys are activated and functioning at a high level or a reduced level. During the first 10 hours after waking up, our kidneys filter fluids at a rapid rate. After this time, their function starts to decrease and they become less efficient at filtering fluids. The kidneys still work, just at a slower pace.

Some researchers recommend consuming most of the fluids during the first 10 hours of the day especially if urinating at night is a concern. It’s important to drink when thirsty, but if already sufficiently hydrated, thatshould help reduce the need to urinate at night.


Can we drink only when we are thirsty?

Thirst serves as a reasonable guide of dehydration. However, it may not adequately keep pace with our body’s hydration needs when we are dehydrated. Also, there are vulnerable groups such as children and elderly people, which have different responses in thermoregulation which places them in increased risk to dehydration (1). It is a good habit to develop to remember to drink plenty of water, especially in warmer climates.


Interested to learn more about hydration? Explore

The benefits of hydration

Hydration and mental health

Hydration and heart failure

Silviya Demerzhan, Ph.D.

Chief Scientific Officer, Nordic Executive Medicine
Medical review by: Dr. Mahir Vazda MD



  1. Popkin BM, D’Anci KE, Rosenberg IH. Water, Hydration and Health. Nutr Rev. 2010 Aug;68(8):439–58.
  2. Drinking water [Internet]. [cited 2023 May 13]. Available from: https://www.livsmedelsverket.se/en/food-habits-health-and-environment/food-and-environment/eco-smart-food-choice/drinking-water
  3. Drinking water [Internet]. 2023 [cited 2023 Jun 23]. Available from: https://www.krisinformation.se/en/hazards-and-risks/drinking-water
  4. Firsov D, Bonny O. Circadian rhythms and the kidney. Nat Rev Nephrol. 2018 Oct;14(10):626–35.