How much water should you drink when it's very hot?

The requirement increases to 2,5-3 liters. Drink often, in small sips, and without waiting for the sensation of thirst.

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When it's very hot, our body's demand for water increases, and we need to take this into account. For a healthy adult, under normal conditions, we're often talking about 1,5–2 liters of water per day, under normal conditions, but with very high temperatures (especially if you sweat) the requirement easily increases up to 2,5–3,5 liters per day, and even more so if you do physical activity or spend a lot of time outdoors.

To calculate the daily water requirement there is a  practical formula often used in nutrition and medicine:

  • 25ml/kg: basic requirement, under normal conditions (sedentary lifestyle, temperate climate)
  • 30ml/kg: more active conditions or warm climate
  • 35 ml/kg (or even more): required when the heat is intense, sweating is heavy, and physical activity is frequent.

For example, an adult weighing 60 kilos needs water, as a minimum hydration, equal to:So your example is correct:

  • 60 kg × 30 ml = 1,8 L under normal conditions
  • 60 kg × 35 ml = 2,1 L when the heat is strong
In any case, water and correct hydration must always be combined with a series of precautions simple, but essential to protect yourself from heavy heat.

Then there is an empirical and practical test to understand when, in the heat, we need more water:

  • Clear or straw-yellow urine: hydration is at adequate levels for our body.
  • Dark urine: you are drinking too little.
  • Intense thirst, headache, tiredness: you are entering a phase of possible dehydration.

An scientific review on heat and physiology of 2024, published in the journalphysiology ofAmerican Physiological Society shows that:

  • the body can lose 0,5–1,5 liters of sweat per hour in conditions of intense heat combined with physical activity
  • the need can therefore increase even more than 4–6 liters/day in extreme cases (outdoor work, sports, heat waves)

Finally, the ways in which we drink when it is very hot also matter:

  • Don't wait until you feel thirsty; your body may already be dehydrated.
  • It is better to drink often and in small sips, with water that is not too cold, to avoid thermal shock.
  • Pay attention to minerals: in case of heavy sweating, in addition to water it is important to replenish mineral salts (sodium, Potassium and magnesium).

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