I am 24 year old girl. I have a computer job in ac and totally sitting kind of. No hard working to burn calories. I was advised to take water 3-4 litre water daily by a HERBALIFE trainer. I searched on google and found it should be only 2-2.5 litre only. I am taking 3-3.5 litre water from last 2 years.
This answer is based on normal situations (examples of an abnormal situations include patrolling in high temperatures in full protective gear, and strenuous exercise, especially in heat/cold) and normal health.
I'm going to go on record here as a renegade who does not believe in an "8 glasses of water a day" (1.9 L) regimen for normal healthy people in normal circumstances. My belief is, if you're thirsty, drink something; make sure at least some of the time, it's water. If you're drinking caffeinated beverages or alcohol, drink a little more water.
Most people will disbelieve this because of the popular press's obsession with 8 8-ounce glasses (1.9 L) per day myth. So some science is in order.
Total water intake includes water in beverages, water in food, and water intake. Daily water needs vary depending on humidity, temperature (sweating), physical exercise etc. But normal, healthy people regulate their daily water balance incredibly well despite changes in size/development (some factors, such as dementia, etc. can interfere with hydration.) In general, as long as food and fluids are readily available, people only need to drink when they are thirsty. (Obviously strenuous exercise, illness, and other special circumstances require a different approach.)
People born around the same time I was spent a large part of their lives never having seen people drink purchased water or toting bottles of water everywhere, and were probably as amused as I was to see the explosive growth of the bottled water industry.
The Institutes of Medicine's Food and Nutrition Board issued a new report in 2004 establishing nutrient recommendations on "water, salt and potassium to maintain health and reduce chronic disease risk". They stated that the vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide. In a press release:
"We don't offer any rule of thumb based on how many glasses of water people should drink each day because our hydration needs can be met through a variety of sources in addition to drinking water," said Lawrence Appel, chair of the panel that wrote the report and professor of medicine, epidemiology, and international health, Johns Hopkins University, Baltimore. "While drinking water is a frequent choice for hydration, people also get water from juice, milk, coffee, tea, soda, fruits, vegetables, and other foods and beverages as well. Moreover, we concluded that on a daily basis, people get adequate amounts of water from normal drinking behavior -- consumption of beverages at meals and in other social situations -- and by letting their thirst guide them."
The report did not specify exact requirements for water, but
set general recommendations for women at approximately 2.7 liters (91 ounces) of total water - from all beverages and foods - each day, and men an average of approximately 3.7 liters (125 ounces daily) of total water.
The panel did not set an upper level for water.
They also stated that caffeinated beverages counted towards fluid requirements:
About 80 percent of people's total water intake comes from drinking water and beverages -- including caffeinated beverages -- and the other 20 percent is derived from food.
How will drinking even more water than necessary benefit people? Many ways. Here are a few that I can think of:
Decreased food intake: drinking a glass of water half an hour before a meal has been shown to slightly decrease the amount of food a person will eat without any distractions.
Decreased spending on high-calorie drinks: drinking water decreases thirst. Maybe the decrease is enough to discourage reaching for unnecessarily high-calorie beverages. Unfortunately water doesn't taste as good as sugary beverages. :(
Increased cardiovascular health: drinking excess water, then using a bathroom several flights up or down from the floor people work on (walking, not using the elevator) will promote a bit of decent exercise several times/day.
Increased spiritual well being: Before drinking, meditating for a few minutes (think about life without clean water to drink, to bathe in, to launder clothes, etc.; imagining a drought seriously impacting people, then thinking about water available for drinking) and experiencing gratitude for the gift of it is beneficial. Gratitude has been shown in many studies to increase happiness.
There are medical conditions wherein drinking more than as guided by thirst is recommended, but that is a different question.
“Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 × 8”?
Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate
Report Sets Dietary Intake Levels for Water, Salt, and Potassium To Maintain Health and Reduce Chronic Disease Risk
Counting blessings versus burdens: An experimental investigation of gratitude and subjective well-being in daily life.
Probably you may safely ignore all those recommendations. Quote from "Medical myths" article published in British Medical Journal):
(...) existing studies suggest that adequate fluid intake is usually met through typical daily consumption of juice, milk, and even caffeinated drinks. In contrast, drinking excess amounts of water can be dangerous, resulting in water intoxication, hyponatraemia, and even death.
About the lack of evidence to the popular 8 glasses / 2 litres recommendation:
The complete lack of evidence supporting the recommendation to drink six to eight glasses of water a day is exhaustively catalogued in an invited review by Heinz Valtin in the American Journal of Physiology.