"Drink eight glasses of water a day" is probably the most repeated health tip there is — and also one of the most vague. How big is a glass? Does coffee count? What about the water in your food? Here is what the guidelines actually say, and a few practical ways to reach your daily amount without it feeling like a chore.
What the official guidelines say
The European Food Safety Authority (EFSA) sets the adequate daily intake of total water for adults at about 2.0 liters for women and 2.5 liters for men. "Total" is the important word: it includes water from all drinks and from food. Food typically covers around 20–30% of it — soups, fruit, vegetables, yogurt and even bread all contain water.
In practice, that means most adults need roughly 1.5–2 liters from drinks on an ordinary day. That's three to four 0.5-liter bottles — which is where the "eight glasses" rule of thumb roughly comes from.
When you need more
Those numbers are a baseline for moderate temperatures and moderate activity. You'll need more when:
- You exercise — you can lose from half a liter to well over a liter of sweat per hour of intense training.
- It's hot or humid — even without exercise, warm weather increases fluid loss.
- You're in dry air — heated offices in winter and airplane cabins quietly dry you out.
- You're pregnant or breastfeeding — EFSA recommends extra fluid in both cases.
- You're unwell — fever, vomiting or diarrhea increase losses quickly.
If you have a heart or kidney condition, your doctor may give you a different target — follow that rather than general guidelines.
What counts toward your daily water
Almost every drink contributes. Plain and sparkling water, tea, milk and flavored water all count. Coffee counts too — at normal amounts, its mild diuretic effect doesn't cancel out the fluid it provides. Sugary sodas and juices also hydrate, but they add a lot of sugar and calories along the way, which is why swapping them for sugar-free options is one of the simplest health upgrades (we compared the two in Sugar-Free Drinks vs Sugary Sodas).
How to tell if you're drinking enough
You don't need to count every sip. Two simple signals work for most healthy adults:
- Urine color — pale straw yellow is a good sign; dark yellow usually means you should drink more.
- Thirst — feeling thirsty is an early signal, not an emergency, but if you're thirsty often, your baseline is probably too low.
Headaches, tiredness and poor concentration in the afternoon can also be early signs of mild dehydration.
Easy habits that help you drink more
- Keep a bottle in sight. People drink noticeably more when water is within reach. A reusable bottle like the INSTICK Glass Bottle (500, 750 or 1000 ml) also makes it easy to track: two 1-liter bottles is your day covered.
- Tie drinking to routines. A glass when you wake up, one with each meal, one when you sit down at your desk.
- Make it taste like something. For many people the real problem isn't forgetting — it's that plain water is boring. One INSTICK Classic stick flavors 0.5 liters of water with no sugar and around 2 kcal per 100 ml, so four sticks a day turn your full 2 liters into something you actually want to drink.
- Rotate flavors. Switching between fruit flavors, Ice Tea and others keeps things interesting. The INSTICK Mix packs are an easy way to find your favorites.
- Plan for training days. After sweaty workouts, water alone doesn't replace lost electrolytes — that's what INSTICK Sport Active is for. See our guide on using Sport Active during workouts.
The bottom line
For most adults, around 1.5–2 liters of drinks a day — more in heat or during exercise — is a sensible target. The best strategy is the one you'll stick to: keep water close, build it into your routine, and make it taste good enough that you reach for it without thinking.
Browse the full INSTICK range — free Omniva delivery on orders over €20.
This article is general information and not medical advice. If you have a health condition, ask your doctor how much fluid is right for you.