Few health topics are surrounded by as much folklore as drinking water. You have probably heard that you need eight glasses a day, that coffee dehydrates you, and that by the time you feel thirsty it is already too late. None of these is quite true. Hydration matters, and some people genuinely need to pay attention to it, but for most healthy adults it is simpler than the marketing suggests.
How much water do you actually need?
The National Academies set general targets for total water intake, which includes water from all drinks and food:
- Men: about 3.7 liters (roughly 15 cups) a day
- Women: about 2.7 liters (roughly 11 cups) a day
That sounds like a lot until you realize that about 20 percent typically comes from food. Fruits, vegetables, soups, yogurt and even bread contain water. Milk, tea, coffee and juice all count toward the rest.
These are averages, not rules. You need more in hot weather, at high altitude, during exercise, when you have a fever, vomiting or diarrhea, and when pregnant or breastfeeding.
The simplest test
For most healthy people, thirst is a reliable guide. Drink when you are thirsty and with meals. Then check your urine. Pale yellow means you are doing fine. Dark yellow, especially first thing in the afternoon, means you could drink more. Clear all day long may mean you are drinking more than you need.
Older adults are the exception. Thirst weakens with age, so people over 65 may need to drink on a schedule rather than waiting to feel thirsty.
Does coffee dehydrate you?
Not in the way people think. Caffeine has a mild diuretic effect, but regular coffee and tea drinkers adapt, and the water in the cup more than makes up for it. Your morning coffee counts toward your fluids. See coffee and supplements for how caffeine affects what you take with it.
What are electrolytes?
Electrolytes are minerals that carry an electric charge when dissolved in body fluids. The main ones are sodium, potassium, chloride, magnesium and calcium. They help control fluid balance, nerve signals, muscle contractions and heart rhythm. MedlinePlus has a clear overview of fluid and electrolyte balance.
The good news is that a normal diet provides plenty of them. Most Americans eat far more sodium than they need. Potassium is the one many people fall short on, and the fix is food: beans, potatoes, bananas, yogurt, leafy greens and tomatoes. Our electrolytes ingredient page and magnesium page go deeper.
When electrolyte drinks and powders make sense
Electrolyte products are marketed as an everyday necessity. For most people, they are not. They can help in these situations:
- Long or intense exercise. If you work out hard for more than about an hour, especially in the heat, you lose sodium in sweat. A sports drink or electrolyte mix can help.
- Heavy sweating at work. Roofers, landscapers, firefighters and kitchen staff in hot conditions may benefit.
- Vomiting or diarrhea. This is where an oral rehydration solution really earns its keep. Products like Pedialyte, or the World Health Organization formula, are designed with the right balance of salt and sugar to help the gut absorb water. For a child who is sick, call your pediatrician for guidance.
- Some medical conditions, but only on your doctor's advice.
If you sit at a desk and walk the dog, plain water is perfect. Many electrolyte powders contain a lot of sodium, which is the last thing most people need, and sports drinks often add 30 grams of sugar or more per bottle.
Reading an electrolyte label
If you do buy one, check:
- Sodium. For long exercise, products with roughly 300 to 600 mg per serving are common. For daily casual use, that is a lot.
- Sugar. A little sugar helps absorption during exercise or illness. For everyday sipping, it is just extra calories.
- Potassium and magnesium. Nice to have, but amounts are usually small.
- Third-party testing, especially if you compete in a tested sport. See what third-party tested really means.
Can you drink too much?
Yes. Drinking very large amounts of plain water in a short time can dilute your blood sodium, a dangerous condition called hyponatremia. It mainly happens during long endurance events like marathons, in people who drink far more than they sweat, and with water-drinking contests. Symptoms include nausea, headache, confusion and, in severe cases, seizures. During long events, drink to thirst and include some sodium.
People with heart failure, kidney disease or liver disease may be told to limit fluids. Follow your doctor's instructions, not general advice.
Signs of dehydration to take seriously
Mild dehydration causes thirst, dry mouth, fatigue, headache and dark urine. Seek medical care for dizziness when standing, confusion, a racing heart, no urination for eight hours or more, or in babies, a sunken soft spot and no wet diapers. The CDC has practical advice on staying safe in extreme heat.
Easy ways to drink more
- Keep a refillable bottle where you can see it.
- Drink a glass of water with every meal.
- Add lemon, cucumber or berries if plain water bores you. See lemon water benefits.
- Eat more water-rich foods, like soups, melons, oranges and cucumbers.
The bottom line
Drink when you are thirsty, drink with meals, and use your urine color as a check. Save electrolyte drinks for long workouts, hot jobs and stomach bugs. If you are older, pregnant or managing a health condition, ask your doctor what is right for you.