How Much Water You Should Really Drink Each Day (and Why 8 Glasses Isn’t the Answer)

You've probably heard that we're supposed to drink eight glasses of water a day. In fact, the recommendation is so widespread that you probably haven't thought to question it. But this guideline doesn't account for numerous factors that impact your body's needs. To learn more, we talked to health experts for insight on how much water to drink per day, along with the signs to look for that you're drinking enough water—or need to drink more.

Why Hydration Matters

When it comes to optimal health and wellness, staying hydrated is key. "Water is essential for nearly every function of the body," says Swapnil Patel, MD, an internist and vice chair of medicine at Hackensack Meridian Jersey Shore University Medical Center. "It helps regulate temperature, transport nutrients, remove waste, and keep joints and tissues lubricated," he notes. 

Water is also necessary for circulating and maintaining blood volume and pressure, providing the structure of cells (and supporting their chemical reactions), promoting digestion and nutrient absorption, and supporting brain function, including cognition and mood, according to Giana DiMaria, MS, registered dietitian and instructor of medicine at New York Medical College.

Hydration is so crucial that even mild dehydration can cause symptoms. The catch? The signs can be subtle. Examples may include thirst, dry mouth, headache, fatigue, dizziness, constipation, reduced urine output, change in urine color, and decreased exercise capacity, says Siera Holley, MS, registered dietitian at The Ohio State University Wexner Medical Center. Also, "it can be easy to overlook hydration status during instances when we don't necessarily feel thirsty, are in colder temperatures, or we aren't noticeably sweating," she adds.

Where Did the 8 Glasses a Day Rule Come From?

The guideline for drinking eight glasses of water per day has circulated for years. "This recommendation originated from the US Food and Nutrition Board in the 1940's based on an average consumption of [about] 2000 calories per day, estimating 1 milliliter per calorie consumed," says DiMaria. Patel adds, "The eight glasses a day rule comes from a recommendation of drinking about 2.5 liters of water daily, but that includes fluids from food, which is often overlooked. Over time, this was simplified into the also familiar '8x8' rule of drinking eight 8-ounce glasses of water per day, which equals about 2 liters or half a gallon," says Patel.

"However, there is no peer-reviewed evidence to support the average recommendation of drinking eight glasses of water a day," says DiMaria. Patel agrees, further confirming that there's no strong scientific evidence that everyone needs this exact amount. "In reality, hydration needs vary, based on body size, activity level, climate, diet, and overall health, so a one-size-fits-all recommendation is impossible," says Patel.

Factors That Impacy Your Water Needs

According to Holley, the factors that impact your daily water needs include:

• Age
• Height
• Weight
• Gender
• Physical activity type, duration, and level
• Certain health conditions
• Some medications
• Climate
• Being pregnant or breastfeeding
• High-sodium and high-protein diets

Specifically, physical activity and heat are the biggest factors that increase water needs, as the body loses more fluid through sweat, Patel says. The same goes at high altitude, where fluid loss accelerates due to faster breathing, says DiMaria.

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What Experts Actually Recommend

So, how much water should you aim to consume per day? Patel says that the National Academy of Medicine suggests 3.7 liters (125 ounces) and 2.7 liters (91 ounces) for men and women, respectively. "Other organizations recommend slightly lower amounts, but the overall range is similar. For most people, staying within roughly 2.5 to 3.5 liters per day is enough to maintain good hydration and support kidney and overall metabolic health," says Patel.

Worth noting, these guidelines include fluids from all sources, not just drinking water. This means other beverages and the food you eat will contribute to your fluid intake, ultimately affecting how many glasses you need to drink to meet your needs.

How to Tell You're Drinking Enough Water

A healthcare provider, such as a primary care physician or registered dietitian, can determine your personalized water needs. There are also some ways to tell if you're drinking enough.

In general, these are the signs that you’re getting enough fluids, according to DiMaria:

• Pale or light yellow-colored urine
• Regular urination every three to four hours
• Stable energy levels
• High skin elasticity
• Good digestion (e.g., no constipation or hard-to-pass stools)

Signs You're Not Drinking Enough Water

There are several things to look for that indicate you might be dehydrated and need more water, notes Patel:

• Dark-colored urine
• Urinating less often
• Dry mouth or tongue
• Increased thirst
• Increased tiredness

In more severe cases, dehydration can also cause sunken eyes and skin that takes longer to return to normal when pinched, says Patel.

Electrolytes

Keep in mind that there's a difference between generally needing enough fluid vs. needing hydration in the form of electrolyte replenishment, DiMaria says. She explains further: "Water is the main source of general hydration for daily needs and overall health, but minerals such as sodium, potassium, and magnesium can help regulate total fluid balance and assist with moving water into the cells." Replenishing electrolytes is especially important during exercise, as well as for people with certain medical conditions when electrolytes are lost via sweat, urine, or gastrointestinal losses, says DiMaria.

Tips to Help You Stay Hydrated

Staying hydrated takes some mindfulness and practice, but it's worth the effort. Holley suggested these tips to help you get enough fluids:

• Set small goals. Aim to drink a certain amount by a specific time of day, which will gradually increase your intake, says Holley. "Logging intake on paper or through an app can help with staying on track," notes Holley.
• Use a reusable water bottle. Keep it nearby throughout the day and take it on the go, says Holley. You can choose one with a straw if that helps you drink more water. "Clear or transparent water bottles can also be helpful because they provide a visual of how much water has been consumed," Holley says.
• Infuse water. "Try infusing water with fruit and herbs, such as lemon, strawberries, and mint leaves, to add flavor without adding sugar,” says Holley.
• Prioritize water-rich foods. Hydrating foods like melons, grapes, bell peppers, tomatoes, cucumbers, and low-sodium soups, broths, and stocks can contribute to daily fluid intake, says Holley.