# The amount of water necessary per day? **URL:** \ **Category:** Factual Questions\ **Created:** [January 20, 2004, 2:36am UTC](https://boards.straightdope.com/t/the-amount-of-water-necessary-per-day/225273 "2004-01-20T02:36:14Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![chaoticbear](https://avatars.discourse-cdn.com/v4/letter/c/f07891/32.png) [@chaoticbear](https://boards.straightdope.com/u/chaoticbear)\ **Post date:** [January 20, 2004, 2:36am UTC](https://boards.straightdope.com/t/the-amount-of-water-necessary-per-day/225273/1 "2004-01-20T02:36:14Z")
I found some sort of advice that said that one should drink a number of ounces of water equal to his body weight in pounds per day. I’m a solid 275, and while I find the “8 glasses a day” reasonable, 2.5 gallons seems like waaay too much. Is it really necessary for me to drink all of that? ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [January 20, 2004, 4:15am UTC](https://boards.straightdope.com/t/the-amount-of-water-necessary-per-day/225273/2 "2004-01-20T04:15:02Z")
Basically, if you’re thirsty, you should drink some water. If you’re not thirsty, don’t worry too much about it. Millions of years of evolution have given us a pretty good feedback mechanism for determining how much water we need. ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [January 20, 2004, 4:34am UTC](https://boards.straightdope.com/t/the-amount-of-water-necessary-per-day/225273/3 "2004-01-20T04:34:28Z")
**ultrafilter** is right. Even the old 8 glasses of water a day is based on a misunderstanding, a rather vital sentence is missed from the original recommendation. [Here](http://www.dartmouth.edu/dms/news/2002_h2/08aug2002_water.shtml) is one discusssion of how it came about. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [January 20, 2004, 4:46am UTC](https://boards.straightdope.com/t/the-amount-of-water-necessary-per-day/225273/4 "2004-01-20T04:46:05Z")
All that said, there may be some good reasons to drink more water than you need. Conventional wisdom holds that drinking lots of water will prevent your body from retaining water. That’s a good thing. And it turns out that drinking water aids in weight loss (see [here](http://my.webmd.com/content/article/79/96070.htm?lastselectedguid=%7B5FE84E90-BC77-4056-A91C-9531713CA348%7D))–not much, but it’s easy, and does help. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [February 17, 2004, 2:54am UTC](https://boards.straightdope.com/t/the-amount-of-water-necessary-per-day/225273/5 "2004-02-17T02:54:49Z")
A new water study just came out: [Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate](http://www.iom.edu/report.asp?id=18495) > [@](#): > > - The vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide. 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. > - 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. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [February 17, 2004, 4:36am UTC](https://boards.straightdope.com/t/the-amount-of-water-necessary-per-day/225273/6 "2004-02-17T04:36:10Z")
For medical and surgical patients, the time-honoured formula to calculate **daily** water requirements is: 100 cc/kg/d for the first 10 kg body weight 50 cc/kg/d for the second 10 kg weight 20 cc/kg/d for every kg thereafter So, an 80 kg person would need 10 X 100 + 10 X 50 + 60 X 20 = 2700 cc/d For a 125 kg (275 lb) person, we’d get 10 X 100 + 10 X 50 + 105 X 20 = 3600 cc/d As an aside, there is some [evidence that drinking “plenty of fluids” leads to a lowered risk of bladder cancer](http://content.nejm.org/cgi/content/abstract/340/18/1390). ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [February 17, 2004, 4:55am UTC](https://boards.straightdope.com/t/the-amount-of-water-necessary-per-day/225273/7 "2004-02-17T04:55:02Z")
KarlGauss gives the necessary recommended fluid requirements per day. This value does NOT include additional fluid for higher than normal work loads or environments. On the other hand, the 100-50-20 formula was designed for children and is presumably less accurate for heavy adults. Also, working kidneys are skillful at extracting water from cola, tea, coffee, juice, fruit and lots of other stuff you eat and drink; so you will survive if you don’t drink your daily gallon of H2O.