How much water do you optimally need to drink in a day?

For as long as I can remember, I have been seeking an answer to one question. And while millions have an answer to this one, they fail to cite any scientific basis for it. It’s probably an answer that you are seeking too. The question under consideration? “How much water do you need to drink in a day to maintain your health and wellbeing?” 

There is no definite or one answer to this. A one-size-fits-all approach can’t be adopted in this case because no two individuals and their needs are alike, and hence their water requirements will vary. 

“Social media often perpetuates a one-size-fits-all approach, but it’s crucial to tailor water intake to personal requirements,” warns Pratiksha Kadam, consultant dietitian at the Kokilaben Dhirubhai Ambani Hospital in Navi Mumbai. There are multiple fluctuations within the human body and the various internal systems that keep us going depending on what we are doing and because of these fluctuations, human body water regulation is also dynamic. This constantly changing, vastly integrated regulatory mechanism, labelled dynamic complexity, is the reason why different people not only have different water requirements, it’s also why our water requirements fluctuate from one day to another.

Most doctors, nutritionists and fitness coaches would ask you to drink anything between three to four litres of water daily, which is the general guideline. “Generally, around 3-4 litres (3.7 litres for men and 2.7 litres for women) per day is a good starting point,” says Chandni Haldurai, head of nutrition at Cult.Fit. “Water needs can vary based on factors such as age, weight, physical activity, and climate. It’s crucial to listen to your body.” Numerous studies have also shown that women usually drink less water than men and it is theorised to be a complex result influenced by female hormones.

What does water do for us?
Water plays an important role in our bodies. It is vital for various bodily functions, including temperature regulation, digestion, nutrient absorption, and joint lubrication. It acts as a transport system, carrying nutrients and oxygen to our cells while flushing out toxins. It also facilitates waste removal and is essential for maintaining overall cellular function. So, adequate hydration is essential for overall wellbeing, good health and productivity.

In 2018, researchers in the United States found that a large number of adults in developed countries did not drink enough water daily. The long-term risks of drinking less water than what we require include cardiovascular problems, obesity and cancer morbidity and mortality, and regulation of glucose metabolism. Observational studies in the last 30 years or so have found that increased daily total water intake reduces the risk of kidney stone formation, stone recurrence, preserves kidney function in chronic kidney disease and retards cyst growth in polycystic kidney disease. Also, a 2021 study conducted by researchers in South Korea found that people who consumed more water were at lower risk of dental problems as well as poor oral health status.

Do tea, coffee, juice and fruit count as water?
It is a valid question considering a plenty of the fruits that we eat are high in water content. Also, there is no tea, coffee, milk or juice possible without water. Kadam says liquids such as tea, coffee and juices do contribute towards our daily water intake but quickly adds that not all beverages are created equal. “Some of the liquids we consume throughout the day can, in fact, lead to dehydration. It’s crucial to balance our various sources of water while monitoring caffeine and sugar intake,” adds Kadam.

As for fruits, doctors and nutritionists say they are a great source of water and minerals and vitamins. “Fruits, such as watermelon, cucumber, orange and strawberries have high water content and contribute to our overall hydration. Including a variety of hydrating foods in your diet can complement your water intake and contribute to up to 20% of your daily water requirement,” says Haldurai. However, water remains the primary source of hydration and one should consume more water than juices, soft drinks, tea and coffee. Haldurai warns that caffeinated beverages and alcoholic drinks can have a diuretic effect, potentially increasing fluid loss and causing dehydration instead.

Bare minimum water intake?
The advice circulating online emphasises the “8×8 rule,” which is to drink eight 8-ounce (240 ml) glasses of water per day, says Haldurai and dismisses it as a “simplistic guideline that may not be suitable for everyone as it is not backed by enough scientific evidence.” While active individuals may require more water to compensate for increased fluid loss through sweating, those leading sedentary lives might need a lot less.

Both Kadam and Haldurai agree that while the bare minimum water need is likely to vary, both recommend drinking at least 2 litres of water per day, which is the general guideline. Drink too little and you end up dehydrated and this could impact your kidney health, physical performance and cognitive functions. And yes, there is something called too much water too. Drink too much and you will come down with a condition called hyponatremia that can dilute electrolytes in the body, potentially causing nausea, headaches, and, in severe cases, life-threatening complications.

“The upper limit is generally considered to be around 3-4 litres per day, but this can also vary based on individual factors. It’s crucial to find a balance that meets your body’s needs. Listening to your body’s thirst signals and adjusting water intake accordingly is key to maintaining optimal hydration levels,” says Haldurai.

When it comes to water, you would do well to not listen to influencers and social media and listen to your body instead.

Shrenik Avlani is a writer and editor and the co-author of The Shivfit Way, a book on functional fitness.