Hydration needs are highly individual and depend on many factors, including your body size and activity level.
Many people follow the 8x8 rule, which recommends drinking eight 8-ounce (237-ml) glasses, or about half a gallon (1.9 liters), of water daily.
However, many believe there are strong health benefits to be gained by increasing your water intake to a full gallon (3.8 liters) per day.
This article takes a look at general water intake recommendations and the potential benefits and consequences of drinking a gallon of water per day.
Perhaps surprisingly, about 60% of your body is water (
Drinking enough water plays an important role in keeping your body healthy and functioning properly.
In fact, almost all of your body’s major systems depend on water to function properly.
Summary Water is essential for vital functions like bringing oxygen to your cells and regulating body temperature.
Water balance is essential for the health and proper functioning of your body. Staying hydrated is critical, but hydration needs are highly individual, so the same recommendations can’t be applied to everyone.
For example, activity level, body size, and how much you sweat are all factors that influence your water requirements and hydration.
Your body knows when you are becoming dehydrated. When your water content decreases, your body tells your brain when and how much to drink — a process known as thirst.
Given that evidence is lacking and many factors affect individual hydration needs, drinking a gallon (3.8 liters) of water per day is likely arbitrary and unnecessary — unless your body requires that much water for proper hydration.
Summary While drinking enough water and maintaining hydration is important, there is limited research to support drinking past the point of quenching your thirst.
Water intake recommendations can vary based on your gender, age, medical condition, and activity level.
Most adults sufficiently meet their fluid needs by letting thirst be their guide.
While there are no specific recommendations on how many glasses of water most adults should drink per day, the Institute of Medicine (IOM) sets recommendations for total water intake.
The IOM suggests that most women meet their hydration needs when consuming 78 ounces (2.3 liters) of total water per day — from both beverages and food — while most men meet their hydration needs when consuming 112 ounces (3.3 liters) per day (
It should be noted that individuals living in hot climates tend to experience increased sweat loss and may need to increase their water intake to stay adequately hydrated.
Prolonged physical activity increases your water loss through sweat.
It’s estimated that athletes lose approximately 6–10% of their body weight through sweat during prolonged athletic events.
However, a water loss of 2% alone can have a noticeable effect on athletic performance (
There is no exact recommendation for how much more water athletes need to drink to maintain hydration. Thus, if you’re an athlete or work out at a high intensity and tend to sweat, plan to replenish your losses with increased fluid intake during and after activity.
Pregnant or breastfeeding women
Women who are pregnant or breastfeeding have significantly increased water needs.
According to the European Food Safety Authority (EFSA), fluid needs are increased by 10 ounces (300 ml) per day during pregnancy (11).
Additionally, it’s important that breastfeeding mothers compensate for the loss of water related to milk production. The EFSA recommends that breastfeeding mothers increase their water intake by about 24 ounces (700 ml) per day (11)
A general recommendation for nursing mothers is to drink a glass of water with every meal and during breastfeeding to help meet their increased fluid needs (
Certain medical conditions may require a restricted water intake to avoid fluid overload, which is when you have too much fluid in your body. Contrarily, other medical conditions may increase your water needs.
Every person’s healthcare needs and conditions are unique. It‘s best to consult your healthcare provider for personalized recommendations regarding your fluid needs.
Summary Water intake recommendations vary based on many factors, including your gender, age, activity level, and medical condition.
Drinking plain water isn’t the only way to meet your fluid requirements.
It’s important to remember that water from other fluids, such as coffee, juice, milk, and tea, count towards your daily fluid intake.
On average, adults get about 80% of their water intake from fluids, while the other 20% comes from foods (
Summary Other fluids and water found in food also contribute to your daily water intake.
There are many benefits associated with drinking enough water. That said, it’s estimated that 16–28% of adults don’t meet their daily fluid needs (
The following are a few of the many benefits of drinking enough water:
- Enhanced exercise performance. Being adequately hydrated can enhance physical performance by preventing fatigue, controlling body temperature, and reducing oxidative stress during intense workouts (
- Keeps you regular. Inadequate water intake has been associated with increased risk of constipation. When there is too little water in the colon, stools harden and become more difficult to pass (
- Weight management. Drinking enough water may affect weight loss by increasing satiety and enhancing metabolic rate. One study found that drinking about 17 ounces (0.5 liters) increased metabolism by 30% (
1, 23, 24).
- Brain function. Maintaining adequate hydration helps your brain function at its best ability. Research demonstrates that even mild dehydration can impair brain function, memory, and cognition in adults (
25, 26, 27).
- Prevents and treats headaches. Dehydration is a common cause of headaches and migraines. Depending on the type of headache, increasing water intake may help relieve headaches in those who are dehydrated (
- Promotes skin health. Increased water intake can help moisturize the skin and increase skin elasticity, keeping it hydrated and healthy (
Summary There are many benefits of drinking enough water, including enhanced physical performance, headache prevention, and improved brain function, skin health, and bowel regularity.
While drinking a gallon of water per day may be appropriate for some people, it may be too much for others.
A good way to know if you need to increase your water intake is to look at your urine. Urine that is dark yellow to amber in color may indicate dehydration, while urine that is pale yellow in color means that you are properly hydrated (
Although water toxicity is rare in adults, drinking an extreme amount of water in a short time can be dangerous.
Drinking too much water too quickly can cause your sodium levels to drop too low. This is known as hyponatremia, which can be serious and even fatal (
However, most adults would have to drink an enormous amount of water fairly quickly for this to happen.
This is an extreme amount of water that would be uncomfortable to tolerate.
To stay hydrated and avoid water intoxication, it’s best to listen to your body. As a general recommendation, drink when you feel thirsty and stop drinking when your thirst is quenched.
Summary Drinking a gallon of water per day may work for some people but could be harmful for others. Although rare, drinking too much water too fast can cause sodium levels in your blood to drop too low, causing a dangerous condition called hyponatremia.
Ultimately, how much water you should drink per day depends on your individual needs.
While there are general guidelines regarding how much water you should drink, they’re to be used as a rule of thumb.
In most cases, it’s best to trust your thirst — drink when you are thirsty and stop when you are not — and use indicators such as urine color to determine if you’re properly hydrated.