How Much Water Should You Drink a Day?

Timing matters, but not in the way you might think. You don't need to chug water at specific times, but there are moments when drinking water is especially helpful.

First thing in the morning is a good time because you've gone several hours without water while sleeping. Your body has been working all night—breathing, maintaining temperature, keeping your organs functioning—and that uses water. Starting your day with a glass helps replenish what you lost overnight.

Before meals is another smart time. Not only does it help you feel fuller (which can help with portion control), but your body needs water to produce digestive juices. Drinking 15-30 minutes before eating gives your body time to prepare for digestion.

During and after exercise, you're losing water through sweat. How much depends on how hard you're working and how long you're at it. A light 30-minute walk might only need a few sips, but an hour-long intense workout could require 16-24 ounces or more. The key is to start hydrated and replace what you lose.

One thing to avoid: chugging huge amounts right before bed. You'll just end up waking up to use the bathroom. Instead, sip water throughout the evening and stop about an hour before you plan to sleep.

Here's something people often forget: you don't have to get all your water from drinking. Food contributes about 20% of your daily water intake, sometimes more if you eat a lot of fruits and vegetables.

Watermelon is about 92% water. A cup of it gives you roughly 5 ounces of fluid. Cucumbers are 96% water—eat a whole one and you've gotten about 6 ounces. Other high-water foods include strawberries (91% water), oranges (87%), and even yogurt (85-88%).

Soups and broths obviously count too. A bowl of chicken soup might give you 8-12 ounces of fluid. Even foods you might not think of, like oatmeal or pasta, contain water that your body uses.

This is why the calculator gives you a total daily water intake recommendation. Some of that will come from food, some from beverages. If you're eating plenty of fruits and vegetables, you might not need to drink quite as much plain water. But if your diet is mostly processed foods, you'll need to drink more.

By the time you feel really thirsty, you're already mildly dehydrated. Your body is pretty good at telling you when something's off, but thirst isn't always the first sign.

One of the easiest ways to check is your urine color. If it's dark yellow or amber, you need more water. Light yellow or clear means you're doing well. Keep in mind that some vitamins and medications can change urine color, so it's not a perfect indicator, but it's a good general guide.

Headaches are another common sign, especially if they come on in the afternoon. Your brain is about 75% water, and when you're dehydrated, it can actually shrink slightly, pulling away from your skull and causing pain. Many people think they need caffeine when really they just need water.

Feeling tired or sluggish, even when you've had enough sleep, can be a dehydration signal. Your body uses water for energy production, and when you're low on fluids, everything slows down. Dry skin, especially on your lips and hands, is another clue.

The good news is that mild dehydration is easy to fix—just drink some water. Severe dehydration is different and needs medical attention, but for most people, paying attention to these early signs and drinking water regularly prevents it from getting to that point.

Most days, your water needs are pretty consistent. But there are times when you need to pay extra attention.

When you're sick: Fever, vomiting, and diarrhea all cause extra fluid loss. You might need an extra 8-16 ounces per day, sometimes more. Electrolyte drinks can help if you're losing a lot through vomiting or diarrhea, but plain water works for most situations.

High altitude: When you're above 8,000 feet, you lose more water through breathing because the air is drier and you breathe faster. Add 16-24 ounces to your normal intake, and pay attention to how you feel.

Airplane travel: Cabin air is extremely dry—often only 10-20% humidity. You're losing water just by breathing. Drink water throughout the flight, and avoid alcohol and caffeine, which make dehydration worse.

Medications: Some medications, like diuretics (water pills), increase urine output. Others, like certain antidepressants, can cause dry mouth. If you're on medication, talk to your doctor about whether you need to adjust your water intake.

Alcohol: Alcohol is a diuretic, meaning it makes you pee more. For every alcoholic drink, you might want to drink an equal amount of water. That's why hangovers are partly about dehydration—your body lost more water than you replaced.