How much water should you drink? Turns out the eight glasses a day recommendation might not be for everyone. A global study now indicates that water consumption depends on the environment, body size, composition and most importantly energy expenditure, with some athletes needing up to 10 litres of water for example.
The study used a deuterium-based water (a traceable form of water that uses an isotope referred to as heavy hydrogen because of an extra neutron in the nucleus) to calculate the intake and loss through a day. It found that the maximum water turnover was seen in men aged between 20 and 30 – an average of about 4.1 litres per day – and women between the ages of 20 and 55 – an average of about 3.1 litres per day. With fat cells containing less water than muscles and organs, water requirement was lower for those with higher body fat content.
The water turnover in women also increases during the third trimester of pregnancy as per the study.
“There is no one-size-fits-all formula — those very physically active such as athletes or those performing manual labour would need more water; those living in hot, humid conditions and sweating a lot would also need more water. Generally, I would say an average of three litres of water should suffice for an adult,” said Dr Rommel Tickoo, Director of Internal Medicine at Max Healthcare.
You get dehydrated when you consume less water than needed but what happens when you consume more? Higher water consumption can cause a condition called hyponatremia – low levels of sodium in the blood because of dilution by the excess water.
“Consuming more water than needed can lead to lethargy, excessive water retention and imbalance in the levels of salts. It can cause hyponatremia or low sodium levels,” said Dr Tickoo.
Dr RP Mathur, senior nephrologist at the Institute of Liver and Biliary Sciences, says that this imbalance in the level of sodium can lead to lethargy, forgetfulness, and in the long term may be associated with dementia.
“In fact, people taking diuretics for high blood pressure are prone to eliminating more sodium through urine – leading to cognitive deficiencies, increased risk of falls and fractures. It is not desirable, which is why diuretics should not be used long-term in a tropical country like ours where there is a lot of sweating too. And, those who do take it should keep checking their sodium and potassium levels, and even their kidney function once a year,” he said.
Lower water consumption on the other hand can lead to dehydration and urinary tract infection, both experts say. Dr Mathur said, “In fact, those with kidney stones, urinary tract infection and constipation must ensure proper water intake because a lower water consumption can lead to more problems such as the kidney stones becoming bigger or newer ones forming or the infection not getting better.”
He added that the elderly should also keep an eye out for their water intake because their thirst mechanism is impaired, meaning they might not feel thirsty even though their body needs the water.
The study looked at not just the environment but also co-related the human development index (HDI) and water consumption. That’s how it found that those living in countries with lower HDI had higher water turnover.
The study, done by researchers from Japan, China, UK, USA, Canada, Norway and many other countries, looked at water turnover in 5,604 people from 26 countries across the globe, test cases being as young as eight-day infants to 96-year-olds. Based on the data, researchers have developed an equation that can be used to predict water usage for an individual. The study, the researchers said, would help in predicting water needs of populations, with as many as 2.2 billion people lacking access to clean drinking water.
Other than the equation of the researchers, how can you estimate whether you are consuming an adequate amount of water? Dr Tickoo suggests a very simple, practical way. “If you are going to the loo three to four times a day and the urine is not yellow, you are doing okay. The colour of the urine should be closer to water, if it is yellow or darker, increase your water intake,” he says.