This article first appeared in Kannada in ಕ್ಷ ಕಿರಣ, Dr Shashikiran Umakanth’s column in the Vishwavani daily. The Inside Story is its English edition. ಈ ಲೇಖನವನ್ನು ಕನ್ನಡದಲ್ಲಿ ಓದಿ
These days, everywhere I look, young men and women are carrying huge one- or two-litre water bottles. The bottles come with marker lines drawn down the side: “This much by 9 am, this much by 1 pm, and finish by 4 pm!”
Recently I asked one of them, half in jest, “What is all this, my friend? Are you going to college, or setting off across a desert?”
The young man answered, quite seriously, “Ayyo, Doctor, you don’t know. An influencer on Instagram said that if you drink four or five litres a day, it washes all the toxins out of your blood and your skin starts to glow! So even when I am not thirsty, I force myself to drink.”
Whenever I hear this, I think of the flowering plants in our front yard.
Suppose you want a plant to grow thick and green, and out of too much love you pour four pots of water on it between morning and evening. What happens? Instead of flourishing, its roots rot, the leaves turn yellow, and the plant dies.
Our bodies are no different. Water is the elixir of life, no doubt. But our elders had a saying, “Even nectar turns to poison in excess”, and water is no exception. Forcing litres of water into a body that does not need it leads to a real medical condition called water intoxication.
The Kidney Story: A Water Pump and a Car Engine
Our two kidneys work rather like the small motor pump that lifts water to the tank at home. In a healthy adult, this pump can get rid of at most about 800 to 1,000 millilitres of water an hour, roughly a litre.
Some people do the arithmetic at once: “Oho! A litre an hour means 24 litres in 24 hours, doesn’t it, Doctor?”
Look at the speedometer of a car. It may say the top speed is 200 kilometres an hour. Drive at that top speed for twenty-four hours without a break, and what happens to the engine? Would it not smoke and give up?
The kidney’s story is the same. That hourly figure is the limit it can reach in an emergency, when it really must. It is not a rate to be kept up all day. In some situations, and naturally as we grow older, the kidneys cannot keep passing such large volumes of urine hour after hour. The extra water then stays in the blood, and that is where the risk begins.
Hyponatraemia, and the Secret of a Good Sambar
So what happens inside the body when we drink far too much water?
Think of the sambar at home. A small pot of it has been boiled just right, with dal, salt and tamarind. Now suppose someone pours two big tumblers of water into it. The salt and the flavour are lost, and you are left with thin, bland water. Don’t take my word for it; try it in your own kitchen today.
Our blood behaves in exactly the same way. When the body is flooded with more water than it needs, sodium, one of the most important minerals in our blood, is diluted, and its concentration falls sharply. In medicine we call this hyponatraemia.
Once the salt in the blood falls, nature follows its own rule. Water moves out of the tiny blood vessels and into the cells around them. You know how a dry raisin left overnight in a bowl of water is plump and swollen by morning? Our cells begin to swell in just the same way.
If the cells of the arms and legs swell a little, the skin stretches and there is no immediate danger. But what about the brain cells, sitting inside a skull as hard as a coconut shell?
Inside the skull, there is very little room for the brain to swell. It begins with headache, vomiting and drowsiness. If things get worse, there can be seizures, loss of consciousness and even coma. Water drunk to make the skin glow can, in some people, end up harming the brain.
The Digital Sensor Built into Your Body
To know how much water you need, you do not need a mobile app or lines on a bottle. Nature has placed in our brain the most precise sensor in the world. It is called thirst.
When the water in our blood runs low, this sensor wakes up at once, dries the throat, and reminds us: “Give me water.”
The other simple guide, one you can see with your own eyes, is the colour of your urine:
- Dark yellow, or the colour of honey: your body is short of water. This is its warning to drink.
- Pale yellow, the colour of dry straw: your water balance is just right.
- Completely clear, like water: you are drinking more than you need and giving your kidneys needless overtime. Put the bottle down for a while!
What About People with Kidney Stones?
There is one important exception to the rule “drink when you are thirsty”: people who have kidney stones, or who tend to form them again and again. They need to drink a little more, so that the salts in the urine do not harden into crystals in the urinary tract.
Their aim should be to pass at least 2 to 2.5 litres of urine a day. Since we usually lose about half a litre of what we drink through sweat, they need to drink roughly 2.5 to 3 litres a day, depending on their daily activity and how much they sweat, or as much as their own doctor advises.
A Last Word of Advice
For healthy people working in an ordinary office, two to two and a half litres of fluid a day is plenty. Remember to count the water in what we eat as well: rice, sambar, buttermilk and fruit all contain a good deal of it.
People who work and sweat in the hot sun, and sportspersons, may need more. Even they are better off not drinking plain water alone, but fluids that also carry salts.
People with heart, liver or kidney disease, however, must drink only the amount their doctor has measured out for them. Otherwise they may run into trouble, anything from swollen legs to hyponatraemia and loss of consciousness.
When you are thirsty, drink until you are satisfied. When you are not, please don’t take social media’s word for it and pour that nectar-like water into your stomach for no reason. Spare your poor kidneys this liquid assault!
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