How Much Water Should You Drink a Day?

Quick Answer: Most adults need about 13 cups (3.7 liters) for men and 9 cups (2.7 liters) for women of total fluids daily—that includes water, other beverages, and the water in your food. But the real answer depends on your body, your activity level, and where you live. The best indicator? Pale yellow urine and feeling good throughout the day.

Why the "8 Glasses a Day" Rule Doesn't Tell the Whole Story

You've probably heard you should drink eight 8-ounce glasses of water daily. It's a nice, memorable number—but it's not based on much science. The Institute of Medicine's actual recommendation, which doctors still reference today, suggests men need about 3.7 liters of total water daily and women about 2.7 liters.¹ That sounds like a lot more than eight glasses, but here's the catch: roughly 20% of your daily water comes from food, especially if you're eating fruits, vegetables, and soups.²

When you account for food, the beverage targets work out to around 13 cups for men and 9 cups for women. Still more than eight glasses for most people, but also not a rigid prescription. Your body is remarkably good at signaling when it needs water—that's what thirst is for. The problem is that many of us have gotten so busy, so distracted, or so accustomed to mild dehydration that we've learned to ignore those signals.

What Actually Changes How Much Water You Need

The baseline recommendations assume you're a moderately active adult living in a temperate climate. Change any of those variables, and your needs shift accordingly.

Exercise is the most obvious factor. When you work out, you lose water through sweat—anywhere from half a liter to over two liters per hour depending on intensity and conditions.³ The American College of Sports Medicine suggests drinking fluids before, during, and after exercise, adjusting based on how much you sweat. A practical approach: weigh yourself before and after a workout. For every pound lost, that's roughly 16 ounces of fluid you need to replace.

Heat and humidity increase sweat losses even when you're not exercising. If you've ever stepped outside on a muggy summer day and immediately felt damp, you understand how quickly your body tries to cool itself. Hot weather can easily double your fluid needs compared to a climate-controlled office.

Altitude matters too. At higher elevations, you breathe faster and lose more water through respiration. You also tend to urinate more frequently as your body adjusts. If you're traveling to the mountains or flying frequently, increase your water intake for the first few days.

Pregnancy and breastfeeding increase fluid needs significantly. Common guidance suggests pregnant women aim for about 10 cups of fluids daily, while breastfeeding mothers may need 12 cups or more.⁴ These are starting points—your healthcare provider can help you dial in a more personalized target.

Hydration and Weight Loss: What the Research Actually Shows

If you're trying to lose weight, staying hydrated isn't just about avoiding dehydration—it may actually help you eat less and burn more. A 12-month study found that overweight women who increased their water intake to more than one liter daily lost an additional 2.3 kg and reduced their waist circumference by 2.3 cm compared to those who didn't change their drinking habits.⁵

Part of this effect comes from simple appetite management. Water takes up space in your stomach, and drinking a glass before meals can help you feel fuller faster. One clinical trial found that people who drank 500ml of water 30 minutes before meals lost more weight than those who didn't.⁶ It's not magic—it's just that a full stomach sends satiety signals to your brain sooner.

There's also evidence that drinking water may temporarily boost your metabolism. A small study published in the Journal of Clinical Endocrinology & Metabolism found that drinking about two cups of water increased metabolic rate by 30% for about an hour.⁷ The effect is modest—not enough to replace exercise or a calorie deficit—but it suggests that proper hydration supports the metabolic processes involved in burning fat.

For a complete breakdown of nutrition strategies that support weight loss, including which foods keep you satisfied longest and how to structure your meals, see our Complete Guide to the Best Foods for Weight Loss.

How to Tell If You're Drinking Enough

Forget counting cups for a moment. Your body gives you feedback that's more reliable than any formula.

Urine color is the simplest check. You're aiming for pale yellow—like light lemonade. If your urine looks like apple juice, you need to drink more. If it's completely clear all day long, you might actually be overdoing it, which can flush out electrolytes your body needs. First thing in the morning, darker urine is normal since you haven't had fluids for hours. By midday, it should lighten up.

Energy and focus often suffer before you notice obvious thirst. Research from Harvard's School of Public Health notes that even mild dehydration can cause fatigue, difficulty concentrating, and mood changes.⁸ If you're hitting an afternoon slump, try a glass of water before reaching for coffee—you might be surprised how often dehydration is the real culprit.

Thirst is a reliable signal for most healthy adults, though it becomes less sensitive as we age. Older adults may not feel thirsty even when they need fluids, which is why checking urine color becomes more important with age.

Yes, Coffee and Tea Count

Here's some good news: your morning coffee contributes to your daily fluid intake. The old belief that caffeine dehydrates you has been largely debunked. While caffeine does have a mild diuretic effect, the water in caffeinated beverages more than compensates for any increased urination.⁹

That said, not all beverages are equal. Plain water is always a solid choice—no calories, no sugar, no additives. Coffee and tea work well too, especially unsweetened. Sugary sodas and juice technically hydrate you, but they come with calories that can undermine weight management goals. One study found that simply replacing one sugar-sweetened beverage per day with water was associated with reduced weight and body fat over time.¹⁰

Hydration for Workouts

If you exercise regularly, your hydration strategy matters more than for someone who sits at a desk all day. Start your workout already hydrated—drink a glass or two in the hour beforehand, spaced out rather than chugged all at once. During exercise, sip to thirst. Most people land somewhere around 12-24 ounces per hour, though this varies widely based on intensity, temperature, and individual sweat rate.

For workouts lasting less than an hour in moderate conditions, water is usually sufficient. For longer sessions, hot environments, or if you're a heavy sweater (you know who you are—the one whose shirt is soaked after 20 minutes), electrolytes help replace the sodium lost in sweat. We cover electrolyte options in detail in our guide to The Best Water Supplements to Make Staying Hydrated Delicious.

For a complete breakdown of how to fuel your workouts for maximum results, including pre- and post-exercise nutrition, check out our Complete Exercise Guide for Weight Loss.

Can You Drink Too Much?

It's rare, but yes. Drinking excessive amounts of plain water—especially during prolonged exercise—can dilute the sodium in your blood to dangerous levels, a condition called hyponatremia. Symptoms include nausea, headache, confusion, and in severe cases, seizures. This is most common in endurance athletes who aggressively hydrate with plain water during long events without replacing electrolytes.

For everyday life, overhydration isn't a major concern. Your kidneys can process about 0.8 to 1 liter of water per hour.¹¹ The issue arises when people force fluids far beyond thirst during extended physical activity. The solution: drink to thirst, add electrolytes for long or hot efforts, and don't buy into the idea that more water is always better.

Making Hydration Easier

Knowing how much to drink is one thing. Actually doing it is another. If you struggle to drink enough water, a few practical strategies help.

Keep water visible and accessible. A bottle on your desk, a glass by your bed, a pitcher in the fridge—the easier water is to reach, the more you'll drink. Some people find that a bottle with time markers helps them pace their intake throughout the day.

Pair drinking with existing habits. A glass when you wake up, one with each meal, one before your workout. Attaching hydration to routines you already have makes it automatic rather than something you have to remember.

If plain water bores you, add flavor naturally. Lemon, lime, cucumber, mint, or berries can make water more appealing without adding sugar or significant calories. Our guide to hydrating foods offers more ideas for getting fluids through your diet.

What to Eat from Clean Eatz Kitchen

Staying hydrated isn't just about what you drink—it's also about what you eat. Meals built around vegetables, lean proteins, and whole grains tend to have higher water content than processed foods. Our Build-A-Meal Plan makes it easy to get balanced, portion-controlled meals that support your hydration goals. Pair them with water-rich sides and you're ahead of the game.

For a grab-and-go option that pairs perfectly with a glass of water or unsweetened tea, try our Protein PB&J—a satisfying snack that won't throw off your nutrition goals.

Frequently Asked Questions

Is 8 glasses of water a day enough?

For some people, yes—but many adults need more. The 8-glass rule is a rough starting point, not a science-backed target. Men generally need about 13 cups of beverages daily, women about 9 cups. Activity level, climate, and body size all affect your actual needs.

Does coffee count toward daily water intake?

Yes. Despite the myth that caffeine dehydrates you, research shows caffeinated beverages still contribute to your daily fluid intake. Just keep total caffeine under 400mg daily and choose unsweetened options when possible.

How do I know if I'm drinking enough water?

The simplest check is urine color—aim for pale yellow. Dark yellow signals you need more fluids. Other signs of good hydration include steady energy, minimal thirst between meals, and regular bathroom visits.

How much water should I drink to lose weight?

Research suggests drinking 1-2 glasses of water before meals can reduce calorie intake and support weight loss. One 12-month study found women who drank more than 1 liter of water daily lost an additional 2.3kg compared to those who didn't increase intake.

Can you drink too much water?

Yes, though it's uncommon in everyday life. Overhydration becomes a concern during prolonged exercise when people drink large amounts of plain water without electrolytes. For long workouts, add electrolytes and drink to thirst rather than forcing fluids.

References

1. Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press; 2005.

2. Centers for Disease Control and Prevention. About Water and Healthier Drinks. CDC Healthy Weight and Growth. Updated March 2025. https://www.cdc.gov/healthy-weight-growth/water-healthy-drinks/

3. Armstrong LE, Johnson EC. Water Intake, Water Balance, and the Elusive Daily Water Requirement. Nutrients. 2018;10(12):1928. doi:10.3390/nu10121928

4. WebMD. How Much Water Should You Drink Every Day? Updated October 2025. https://www.webmd.com/diet/how-much-water-to-drink

5. Stookey JD, et al. Drinking water is associated with weight loss in overweight dieting women independent of diet and activity. Obesity. 2008;16(11):2481-2488. doi:10.1038/oby.2008.409

6. Parretti HM, et al. Efficacy of water preloading before main meals as a strategy for weight loss in primary care patients with obesity. Obesity. 2015;23(9):1785-1791.

7. Boschmann M, et al. Water-induced thermogenesis. J Clin Endocrinol Metab. 2003;88(12):6015-6019.

8. Harvard T.H. Chan School of Public Health. The Nutrition Source: Water. https://nutritionsource.hsph.harvard.edu/water/

9. Harvard Health Publishing. How much water should you drink? Harvard Medical School. https://www.health.harvard.edu/staying-healthy/how-much-water-should-you-drink

10. Fresán U, et al. Substitution Models of Water for Other Beverages, and the Incidence of Obesity and Weight Gain in the SUN Cohort. Nutrients. 2016;8(11):688.

11. Popkin BM, D'Anci KE, Rosenberg IH. Water, hydration, and health. Nutr Rev. 2010;68(8):439-458.