When the thermometer exceeds 35°C, the same sentence comes up everywhere: “drink 2 liters of water per day“. This benchmark is reassuring, but it does not fit in all situations, especially in heatwaves, when dehydration lurks. Between magic numbers and the reality of working days, there is a gap that can be costly to the body.
Dr. Sarah Rebert, aka @doctorgoodtips on Instagram, explains that “the right water figure is not the same for everyone“. This doctor points out that 2 liters may be enough for someone who stays cool, but may be too little for someone who works outside or runs under 35°C. She summarizes her position: “The goal is not to drink as much as possible. It’s about drinking regularly, adapted to your losses.“
Heatwave: the amount of water really depends on your sweating
For Dr Sarah Rebert, it’s all about what you lose. Sweating is the body’s primary way of cooling itself, and the more you sweat, the greater your needs. A person resting in a cool home does not have the same needs as a delivery person on a bicycle in direct sunlight. The volume of water should follow your day and the heat, not the other way around.
To know if you are drinking enough, this doctor offers a simple benchmark: your urine. When they remain clear and regular, it is rather reassuring; if they become dark or rare, the body is probably lacking water. She also recommends not waiting until you are very thirsty to drink, especially in a heatwave. In case of long and heavy sweating, you also lose salt, hence the occasional benefit of drinks with electrolytes.
Heatwave: how much to drink in practice depending on your day?
The numerical benchmarks remain useful, provided they are adapted. Our body needs around 2.5 liters of water per day, part of it coming from food, and we recommend 1.5 to 2 liters to drink in normal times, rather 2 to 2.5 liters in the event of a heatwave, or even more if we move around a lot. You need at least half a liter more, up to 2 to 3 liters, or about one glass per hour.
In practice, someone who stays cool and doesn’t go out much can aim for the lower end of these ranges, monitoring urine color. A person who walks a lot or works outdoors should move closer to the high zone, while splitting their intake. Drinking a little every hour fits well with Dr Sarah Rebert’s idea: adjust the amount of water you drink to what you really sweat.
Heatwave: what drinks to choose to stay well hydrated?
It is advisable to favor still water, served cool or lukewarm rather than iced or hot, possibly flavored with lemon. Alcoholic drinks, very sugary sodas or industrial juices hydrate poorly and do not count towards the recommended 2.5 liters of water.
In the event of headaches, extreme fatigue or nausea, get cool, drink in small sips and call 15 or 18 if the discomfort persists.