How Much Water Should You Drink Every Day? (Backed by Science)

Water is essential for life. Without water, humans can only survive for a few days. 75% of the total body weight in infants to 55% in elderly comprises of water.

All the chemical reactions that are essential for maintaining human life take place in the body’s water. However, we always tend to forget about the most essential component of the body and the diet, which is ‘water’.

How much body water we lose per day and how?

At rest, the body loses water in the following forms:

Sweat: Sweating is the body’s natural cooling system. A large source of water loss in the human body is through sweating. In simple words, the more you work out or the more physically active you are, the more water you lose. Hence, the requirement of water in such individuals is higher.

Approximately 5% of water from the body is lost through sweat. On an average, water lost through sweat can be 450 mL/day, but during physical activity in hot climate 3 liters loss per hour is also possible.

Urine: A healthy human loses around 60% of the water via urine. The urine output generally ranges 1000-2000 mL/day, but it can be altered by heat strain and exercise.

If your water intake is high, your kidneys will produce more urine, but if your water intake is less, small amounts of concentrated urine are produced by the kidneys.

Less water intake or severe dehydration can damage the kidneys. Therefore, it is important to stay hydrated.

The color of the urine is an indicator of hydration. Colorless or light-yellow urine indicates hydration, whereas dark yellow urine is a sign of dehydration.

Feces: 5-7% water from the body is lost via feces. The gastrointestinal and fecal water output accounts for 100-300 mL/day.

Water is important for a healthy digestion and to prevent constipation. If you drink less water, your large intestine will absorb water from your food waste, thus leading to constipation.

Lungs: Hydration is the key to the healthy respiratory system. The body loses 15-16% water from the lungs. In other words, respiratory water loss averages 250-350 mL/day in sedentary adults and 600 mL/day in individuals who are physically active.

While breathing, the water evaporates from the respiratory tract, hence it is also known as insensible water loss because we are unaware of it.

Summary: The total water loss is estimated to be approximately 1500-3100 mL/day for adults in temperate climates, says research. (1, 2, 3, 4)

Why Should We Drink Water?

Drinking water is important to restore the required water level in the body and compensating the lost water. It also has other benefits, as below:

Improves Brain Function

Staying hydrated or dehydrated can influence the brain function. Studies state that mild levels of dehydration can produce disruptions in mood and cognitive functioning.

Mild dehydration can alter the level of concentration, alertness and short-term memory in all age groups. It can further increase the feelings of fatigue and anxiety, which can interfere with a person’s ability to perform cognitive tasks.

Not drinking adequate water increases sleepiness and confusion. This may result in poor cognitive performance and lack of interest in performing normal daily activities. (5, 6)

Prevents Headache

Water-deprivation headache is common in which, pain arises from the meninges. Meninges are the protective tissues that cover the brain and the spinal cord. This indicates that such a headache also involves the brain and impairs cognition and increases irritability.

Because dehydration triggers headache, increased water intake could help, reports a study. Water intake reduces fatigue, increases alertness and makes a person feel fresh, which can help in relieving headache. (7, 8)

Relieves Constipation

Mild dehydration is a risk factor for constipation. A decrease in the water content increases the viscosity of the stools, thus making it difficult to pass. It further increases the colonic transit time and causes long duration contractions.

Adequate water intake is recommended for constipated children, adults and elderly. Water intake softens the stools, reduces the colonic transit time and helps in the easy passage of stools without adding any stress on the digestive tract. (9)

Improves Physical Performance

Dehydration impairs an individual’s physical performance. A decrease in the body water level provokes changes in the cardiovascular, thermoregulatory, metabolic and central nervous system function.

It increases fatigue and impacts a person’s ability to perform work negatively. Dehydration in athletes or sportspersons can hamper their performance. It reduces motivation, increases perceived efforts, decreases blood pressure and blood flow to the muscles.

Therefore, athletes must drink plenty of water before and after their performance to replenish the lost water stores. (10)

Boosts Kidney Function

Drinking less water makes the urine concentrated, alters its colour and increases its odour. This increases the risk of developing kidney stones. By drinking adequate water, you can prevent the onset of kidney stones.

Kidneys require water for the removal of waste products from the body through urine and feces. If the body water levels drop, a load of toxic substances on the kidneys increase. This can damage the kidneys and alter its functioning too.

Studies have found that inadequate water intake can increase the risk of kidney injury from pesticides, heavy metals, agrochemicals and other potential exposures. Hence, it is important to drink plenty of water in order to prevent the kidneys against damage. (11)

Enhances Skin Health

Studies have noted a positive association between water intake and better skin performance. Water is the most effective and inexpensive way to boost skin health.

Water deficiency is associated with several dermatological dysfunctions. Furthermore, research has found that dietary water intake affects the skin in the same way as a topical moisturizer.

It improves the elasticity of the skin and makes it soft and supple. Dietary water intake also moisturizes the skin and prevents dry and rough skin. It improves the skin health and boosts the supply of nutrient and oxygen-rich blood towards the skin.

Keeping the skin well hydrated makes the skin look younger and healthier. Besides this, drinking water helps in flushing out the toxins and other harmful compounds and thus gives the skin a clear look. (12)

How Much Water Should You Drink Every Day?

It is often said that 8-10 glasses of water are required for a healthy body, but this is not true for everyone. The amount of water required depends upon the following factors:

Climate: – During summer season your body temperature increases, and you sweat more, hence, your body requires more water.

Age: – Older persons are less thirsty and they drink less fluids as compared to younger ones. This is because older persons have diminished thirst sensation, which leads to reduced water consumption.

Physical activity: – People who are more physically active require more water. Athletes or sportsperson sweat more, which helps the body to cool down. Hence, their requirement for water increases.

Medical condition: – If you are dehydrated due to diarrhea and vomiting, your body needs more water. But in case of heart failure or kidney diseases, you may need to restrict your water intake. Your physician will adjust your fluid intake as per your medical condition.

Hence, the total water intake for adult sedentary females and males is between 2000mL – 3000mL. (13)

When should you drink water?

• It is important to drink water all throughout the day for your body to function properly.
• Drink 1-2 glasses of water on waking up. This helps to rehydrate and refresh your body, flush out the toxins and relieve constipation.
• Some studies report that drinking water 30 minutes before eating your meal may make you feel full and aid in weight loss.
• Avoid drinking a lot of water before going to bed. This may lead to frequent urination at mid-night and sleep disturbances. Don’t drink more than one cup of water before going to bed.
• Before workout: Drink water before an exercise to guard against heat stroke and dehydration. Dietary water intake also improves physical performance and ability to concentrate on the task.
• Post workout: After a workout or exercise session it is important to drink plenty of water to replenish the lost fluids through sweat or urine. The amount of water you need to drink depends upon the climatic conditions and the duration of exercise. Don’t drink cold water after physical workout. Lukewarm or normal water should be fine and recommended.
• Drink water sip by sip and slowly. Don’t be in hurry to drink water quickly.
• Do not drink water between the meal. Downing glasses of water along with the meal can interfere with the digestion of food and cause stomach cramps and indigestion. It can dilute the digestive juices and hinder the breakdown of food. (14)

Why should we not drink cold water?

• Drinking cold water has a deleterious effect on the heart rate or cardiac rhythm, especially in patients with acute myocardial infarction. Studies report that ice water ingestion can decrease heart rate. It stimulates the vagus nerve and reduces the heart rate.
• An old study observed that drinking cold water is associated with upper respiratory tract viral infections. It causes nasal congestion, sore throat and overproduction of mucus. It also disturbs the body’s balance of hot and cold.
• Another interesting study observed that cold water is devoid of many essential minerals that could become unfavorable to the digestive tract. These minerals are essential for keeping the digestive tract healthy. Drinking cold water along or after a meal can harden the oil in the foods consumed and create a fat deposit in the intestine. Replacing a glass of cold water with a glass of warm water improves the digestion of food and improves bowel movements too. (15, 16)

Edited By: Dr. Jagdev Singh