You already know the refrain: "drink 1.5 liters of water a day, especially in summer." Except that when the terraces in Brussels show 34 degrees, you spend two days in a row at a festival, 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 at all. 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 to really drink, and especially when plain water becomes insufficient. No medical jargon, no generic list. Just what works.
Why summer completely changes the game when it comes to 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 groggy even after drinking huge amounts of water. You've replenished the water but not the accompanying minerals. As a result, your body can't properly reabsorb the liquid you just drank, and some of it goes straight back out in the toilet.
That's the real issue with staying hydrated in summer. It's not how much you drink, but what you drink and how your body uses it. Someone who sweats a lot and drinks only water may end up feeling more tired than when they started 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 showing that you're already dehydrated
Dehydration doesn't warn you. 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 those. Add to them the feeling that the heat won't go down 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 a conversation. Nighttime calf cramps. Mood swings and easy irritability. All these signs often point to mild chronic dehydration - the kind that won't land you in the hospital but ruins your days without you making the connection. If you check two or three of them during a heat wave, you have your answer.
How much to really drink when it's hot
The 1.5-liter rule is a universal baseline, not a target for everyone. A sedentary adult in Belgium in July will need approximately 2 to 2.5 liters of fluid per day. As soon as you add physical activity, even something moderate like a one-hour bike ride, you need to count on an additional 500 ml to 1 liter. If you do intense exercise or stay in the sun for a long time, you can easily reach 3 to 3.5 liters in a day.
A simple way to measure without calculating: look at 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, transparent urine probably means you've drunk too much plain water and diluted your minerals, which isn't ideal either.
And don't forget: fluids don't come only from water. A cup of tea, a bowl of cold soup, a yogurt, a watermelon - all of that counts toward the total. Seasonal fruits and vegetables can easily cover 20 percent of your daily fluid 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
This is the point no one explains clearly. Plain water does the job for a normal work-from-home day with the air conditioning on. As soon as you move outside that framework, it shows its limits. In practical terms, water becomes insufficient when you sweat for more than 30 minutes straight, when the temperature exceeds 28 degrees in the shade for several hours, or when you engage in intense physical effort.
What's missing in those moments 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 proper hydration to take place.
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 don't replace your water; you make it usable by your body. It's the difference between swallowing fuel without an engine and swallowing fuel in 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.
And if you want to compare the formats, sugar-free sticks or coconut water drinks, they're side by side in our electrolyte collection.
Drinks to avoid in summer, even if they seem refreshing
Not all cold drinks hydrate. Some even make the situation worse. Regular sodas contain 25 to 35 grams of sugar per can, which requires additional water to be metabolized. You drink to make up for a loss, and 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 heat wave rarely have another explanation. That doesn't mean you have to ban terrace drinks; it means you should follow every glass with a bottle of water to stay afloat.
Iced coffee by the gallon is the same story, even in a lighter version. As a mild diuretic, it makes you lose a little more liquid than it provides. One or two a day is fine. 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, disguised by sporty branding. Read the labels. If you see more than 5 grams of sugar per 100 ml, move on.
Practical 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 lost 300 to 500 ml overnight, so make up for it.
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 water bottle. Once you've tried it, you won't go back. The difference in recovery is obvious.
For festivals, plan on one stick in the morning when you wake up, one in the late afternoon, and one before bed. Couleur Café, Dour, Tomorrowland, the rule is the same: you dance for eight hours in 32-degree heat, so you can't expect to keep going on beer and three sips of water.
During heat waves, eat water-rich fruits 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've explained 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
Allow for 2 to 3 liters of total fluids per day for a normal adult, and up to 4 liters if you combine a heatwave with physical activity. No need to be exact, but clearly go above the usual 1.5 L.
Are electrolytes useful if I don't exercise
Yes, whenever you sweat a lot: a heatwave, a crowded metro ride, an entire afternoon on a sunny terrace, a festival, or a long car journey without air conditioning. You don't have to be a marathon runner to lose minerals.
Can you rehydrate by eating fruit
Partly, yes. Watermelon, cucumber, strawberry and melon are made up of more than 90 percent water and also contain potassium. They complement your hydration but don't completely replace what you drink, especially in hot weather.
Does sparkling water hydrate as well as still water
Yes, sparkling water hydrates just as well. The only difference is digestive comfort (some people feel bloated from carbonation) and the sodium content of some sparkling waters, which can be high. For everyday hydration, still or sparkling, it's 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. Its 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. Sugar-free, 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, check out the Buddy cans, with natural, organic caffeine and 13 kcal per 100 ml, perfect for getting through long days without the sugary junk found in classic energy drinks.
Summer is already here, so you might as well get through it properly hydrated.
