You already know the refrain: "drink 1.5 liters of water a day, especially in summer." Except that when the terraces of Brussels are showing 34 degrees, you are doing two days of a festival back to back, or you run at 7 p.m. because you couldn't find an earlier time slot, the 1.5-liter rule is no longer enough.
Not even close. This article starts from the beginning: what happens in your body when it's hot, the signs that 90 percent of people ignore, how much you really need to drink, and above all, when plain water becomes insufficient. No medical waffle, no generic list. Just what works.
Why summer completely changes the game for your hydration
When it's hot, your body doesn't just lose water. It also loses salt, potassium and magnesium through sweat. That's why after a heavy sweating session you can feel foggy even if you've drunk a huge amount of water. You've replenished the water but not the minerals that go with it. As a result, your body can't properly reabsorb the liquid you've just swallowed, and some of it goes straight back out through the toilet.
That's the real issue with summer hydration. Not how much you drink, but what you drink and how your body uses it. Someone who sweats a lot and drinks only water can end up feeling more tired than they did at the start, because the concentration of minerals in their blood drops. English speakers call this hyponatremia, and it happens more often than you might think, particularly among amateur runners who go through bottle after bottle of plain water without ever thinking about electrolytes.
The signs that show you are already dehydrated
Dehydration doesn't give you any warning. When you feel thirsty, you've already lost around 1 to 2 percent of your body weight in water. In other words, you're already behind.
The obvious signs you shouldn't ignore
Dry mouth, urinating less often, very dark urine, thirst that becomes constant. Everyone knows these. Add the feeling of heat that doesn't go away when you go back inside, and you've got the classics.
The lesser-known signs that fool everyone
A headache at the end of the day even though you haven't done anything unusual. Fatigue setting in around 3 or 4 p.m. for no apparent reason. Difficulty concentrating on your work or on a conversation. Nighttime calf cramps. Mood swings, easy irritability. All these signs often point to mild chronic dehydration, the kind that doesn't send you to the hospital but ruins your days without you making the connection. If you tick two or three of them during a heatwave, you've got your answer.
How much to drink when it's hot
The 1.5-liter rule is a universal minimum, not a target for everyone. A sedentary adult in Belgium in July will need around 2 to 2.5 liters of liquid per day. As soon as you add physical activity, even something moderate like a one-hour bike ride, you need to add another 500 ml to 1 liter. If you do intense exercise or stay in the sun for a long time, you can easily reach 3 or 3.5 liters in a day.
A simple way to measure it without doing any calculations: check the color of your urine in the middle of the day. If it's pale yellow, like light straw, you're good. If it's dark yellow, like tea, you're behind. Clear or transparent means you've probably drunk too much plain water and diluted your minerals, which isn't ideal either.
And don't forget: liquid doesn't only come from water. A cup of tea, a bowl of cold soup, a yogurt, a slice of watermelon - all of it counts toward the total. Seasonal fruit and vegetables can easily cover 20 percent of your daily hydration needs when you eat enough of them.
These signs don't lie. We listed seven of them in our article on electrolyte deficiency.
When plain water is no longer enough and why
Here's the point no one explains clearly. Plain water does the job on a normal work-from-home day with the air conditioning on. As soon as you step outside that framework, it shows its limits. In practical terms, water becomes insufficient when you sweat for more than 30 minutes continuously, when the temperature exceeds 28 degrees in the shade for several hours, or when you do prolonged strenuous physical activity.
What you're missing at those times is the trio of potassium, magnesium and sodium. These three minerals are responsible for transporting water into your cells, nerve transmission and muscle contraction. Without enough of them, your body doesn't know what to do with the water you give it. That's why electrolytes matter: they reset the balance and allow your body to actually hydrate.
That's exactly the role BUDDY sticks play. Potassium, magnesium, sea salt, soluble fiber, no sugar, two flavors (Mint Lemon and Citrus Peach), to mix into a bottle of water. You aren't replacing your water, you're making it usable by your body. It's the difference between pouring fuel into an engine-less car and pouring fuel into a car.
To find out when a mineral drink is genuinely justified and when a glass of water is enough, our electrolyte drink guide sorts it all out.
The drinks to avoid in summer even if they seem refreshing
Not every cold drink hydrates you. Some even make things worse. Regular sodas contain 25 to 35 grams of sugar per can, which requires extra water to be metabolized. You drink to make up for a loss, but you actually create an additional loss.
Alcohol is clearly summer's number one enemy. As a diuretic, it sends you to the bathroom faster than you can absorb it, and difficult mornings during a heatwave rarely have any other explanation. That doesn't mean you have to ban terrace drinks; it means you need to pair every drink with a bottle of water to stay afloat.
Iced coffee by the gallon is the same story in a lighter version. As a mild diuretic, it makes you lose slightly more liquid than it provides. One or two a day, no problem. Six is a one-way ticket to a headache at 5 p.m.
And be especially wary of "hydrating" drinks marketed as such on supermarket shelves. Some contain as much sugar as a Coke, hidden behind a sporty image. Read the labels. If you see more than 5 grams of sugar per 100 ml, leave it on the shelf.
Practical good habits to adopt right now
Here's the actionable summary we wish we'd received before every summer.
Start your day with a large glass of room-temperature water, before coffee. Your body loses 300 to 500 ml during the night, so make it up.
Keep a 750 ml or 1-liter bottle within reach at all times. On your desk, in your bag, in the car. The visual reminder does 80 percent of the work.
When you exercise in hot weather, add an electrolyte stick to your bottle. Once you've tried it, you won't go back. The difference in recovery is obvious.
For festivals, plan on one stick when you wake up, one in the late afternoon, and one before bed. Couleur Café, Dour, Tomorrowland, the rule is the same: you're dancing for eight hours in 32-degree heat, so you can't expect to get through it on beer and three sips of water.
During heatwaves, eat water-rich fruit and vegetables with every meal. Cucumber, watermelon, tomato, melon, zucchini. They're your silent allies.
Listen to your fatigue. If you feel an unexplained slump in the middle of the afternoon, try a glass of water with electrolytes before reaching for coffee. Nine times out of ten, that's what was missing.
During a heatwave, the guidelines change again. We explain them in detail in our article on what to drink during a heatwave.
Summer hydration FAQ
How many liters of water per day during a heatwave
Count on 2 to 3 liters of total liquid per day for an average adult, and up to 4 liters if you combine a heatwave with physical activity. There's no need to be precise to the milliliter, but clearly go above your usual 1.5 L.
Are electrolytes useful if I don't exercise
Yes, whenever you sweat a lot: a heatwave, a crowded subway commute, an entire afternoon on a sunny terrace, a festival, or a long car journey without air conditioning. You don't need to be a marathon runner to lose minerals.
Can you rehydrate by eating fruit
Partly, yes. Watermelon, cucumber, strawberries and melon are more than 90 percent water and also contain potassium. They complement your hydration but don't completely replace what you drink, especially in very hot weather.
Does sparkling water hydrate as well as still water
Yes, the hydration is identical. The only differences are digestive comfort (some people get bloated from sparkling water) and the sodium content of certain sparkling waters, which can be high. For daily hydration, still or sparkling is up to you.
Our electrolyte powder provides 252 mg of sodium, 300 mg of potassium and 56 mg of magnesium per stick, with no sugar. Their contents are compared with those of other brands on drinkscore.info.
Take action without overthinking it
This summer, stop improvising your hydration. A bottle of water, an electrolyte stick when you sweat, fruit with every meal and a proper look at the color of your urine in the middle of the day. It's as simple as that.
If you want to try them, our electrolyte powder comes in boxes of 10 sticks for 15 euros, in Mint Lemon or Citrus Peach. No sugar, with potassium, magnesium and sea salt. You'll feel the difference from the first really hot day.
And if you're looking for a natural boost instead, take a look at the Buddy cans, with natural organic caffeine and 13 kcal per 100 ml, a good companion for long days without the sugary gunk found in classic energy drinks.
Summer is already here, so you might as well experience it properly hydrated.
