How Much Water Do You Actually Need?
Where the Eight Glasses Myth Came From
Everybody repeats it. Almost nobody can tell you where it comes from.
The most likely origin is a 1945 recommendation from the US Food and Nutrition Board suggesting about 2.5 litres of water a day for adults. The very next sentence — the one that never gets quoted — noted that most of this quantity is contained in prepared foods.
That second sentence disappeared, and a guideline about total water intake turned into an instruction to drink eight glasses on top of everything else.
It is not harmful advice. It is just imprecise, and it ignores that you are a different size, in a different climate, doing different things than the person next to you.
A Number That Actually Fits You
A far more useful starting point is 30-35 ml per kilogram of body weight.
Worked through:
- 55 kg → roughly 1.7-1.9 litres
- 70 kg → roughly 2.1-2.4 litres
- 90 kg → roughly 2.7-3.1 litres
Then adjust upward for the things that genuinely increase your losses:
- Exercise — add 500-700 ml per hour of real sweating
- Indian summer — add 500 ml to 1 litre on hot days, more if you are outdoors
- Air conditioning all day — add around 300 ml; dry recirculated air pulls more moisture from you than people realise
- Coffee or tea in quantity — mildly diuretic, though far less than commonly claimed
At around 95 kg and working in an air-conditioned office, my own target landed at 3 to 3.5 litres. On days when I walk in the evening heat it is closer to 4.
Stop Using Thirst as Your Signal
By the time you feel thirsty you are already at roughly 1-2% dehydration — and at that level performance and concentration have already dropped measurably.
The reliable indicator is much simpler, and you check it several times a day anyway.
Urine colour:
- Pale straw, almost clear — well hydrated
- Light yellow — fine
- Dark yellow — drink now
- Amber or darker — significantly dehydrated
One caveat worth knowing: B-vitamin supplements turn urine bright yellow regardless of hydration, so if you take a multivitamin, judge by the first urination of the day before the supplement.
The other signal I learned to trust is the mid-afternoon energy dip. Mine was almost always mild dehydration rather than genuine tiredness. A glass of water solved what I used to solve with a third cup of tea.
What Being Short on Water Was Costing Me
These are the effects I noticed once I actually corrected it — and I only recognised them in hindsight.
Hunger that was not hunger. The hypothalamus regulates both thirst and hunger, and the signals get confused easily. I now drink a glass of water and wait ten minutes before eating between meals. Perhaps half the time the "hunger" simply disappears.
Headaches. I had assumed screen fatigue. Some of it was, but the frequency dropped noticeably once I was consistently at 3 litres.
Constipation. Fibre without adequate water actually makes this worse, not better. Adding more salad while under-drinking was the wrong half of the fix.
Worse workouts. Even 2% dehydration reduces strength and endurance meaningfully. I could feel the difference between a well-hydrated evening walk and a badly hydrated one.
Dull skin and dry mouth on waking — the most obvious signals, and the ones I ignored the longest.
How I Actually Drink Three Litres
Knowing the number was never my problem. Hitting it was. These are the things that worked.
Anchor water to events, not to the clock. A glass on waking, one before each meal, one when I sit down at my desk, one after every call. Habits attached to something you already do survive; reminders on a phone do not.
One large bottle, not a small glass. I keep a 1-litre bottle and aim to finish three. Counting to three is easy. Counting to twelve small glasses is not.
Keep it out of arm's reach. As with the desk-job problem, putting the bottle across the room means every refill is also a short walk.
Two glasses immediately on waking. You have gone seven or eight hours without anything. This is the easiest litre of the day and it sets the tone.
Make it interesting when plain water gets boring. Lemon, mint, cucumber, a few soaked saunf seeds. Nimbu paani without sugar. Coconut water genuinely counts and adds potassium.
And a note on what does not count the way people hope: sweetened tea, coffee in large volumes, and packaged juices come with sugar or caffeine attached. Buttermilk and plain chaas, on the other hand, count perfectly well and are among the better summer options we already have.
You Can Drink Too Much
This is rare, but it is worth stating plainly because the internet tends to treat water as risk-free.
Drinking extreme quantities in a short period — several litres in an hour or two — can dilute blood sodium to a dangerous degree. It is called hyponatraemia, and it has killed people, mostly endurance athletes drinking aggressively during long events.
For practical purposes: spread your intake across the day rather than forcing large volumes at once, and if you sweat heavily for hours, replace some salt too, not only water. Regular Indian food usually takes care of that without any effort.
If you have kidney or heart conditions, your fluid target is a medical question, not a general one. This is my experience and my reading, not medical advice.
The honest summary: water was the cheapest and least interesting change I made, and it quietly improved my hunger, my headaches and my energy more than several things I had put far more effort into.