8 Glasses of Water?

Take Home Action?

Drink water. Some. Do you need 8 x 8oz (1.9l) per day? No. Include tea and coffee in your consumption figures.

Do not drink sweetened sugar beverages. (SSB). That means avoid gin and tonic, rum and coke or any alcohol with SSB’s. change to Just do it on the rocks.

Science Behind the Numbers

Dr Karl from the Australian ABC says:

You see them everywhere. Those ubiquitous bottles of water, it seems, are an absolutely essential part of many people’s lives. Presumably, without this life-giving bottled water, people wither up, die and turn into a pile of dust waiting to be blown away by the next breeze. You come across the exhortation to “drink at least eight glasses of water a day” everywhere. This advice has been in a health column in the New York Times, and published by many writers in the popular press. It even appears in a pamphlet from the University of California Los Angeles, which advises the students to “carry a water bottle with you. Drink often while sitting in class…”

Another part of the “eight glasses of water per day” story is that we are all chronically dehydrated, and yet our bodies are not sensitive enough to correct this by making us thirsty. From a physiological point of view, this is rubbish.

The conventional advice is that average individual needs at least 1ml of fluid for every calorie burned. That’s approximately eight 8-oz glasses per day for a 2000 calories diet, or 8x8oz It is (a) based on panel advice, but there is little science to back this up.  You are likely to have to go to the toilet regularly.  While adequate hydration is essential for maintaining blood volume, kidney function, and preventing constipation (b), you get lots of water from green leafy vegetables and fruits. If you eat processed foods, then your requirement may be higher. Furthermore the admonition not to count coffee and tea or beer is also wrong.

Does drinking water have some benefits? Importantly, don’t substitute sugar sweetened beverages (SSBs) for water. Water has no calories or additives, is widely available, inexpensive and generally safe. Epidemiological studies show that energy intake is significantly lower (~9%, or 194 kcal/d) in water drinkers compared to non-water drinkers. German school-children, in just one year drinking water rather than SSBs, reduced the risk of being overweight by 31%. As well has no calories, food is not over compensated for at subsequent meals.  Consuming water before or with a meal reduces feelings of hunger and increases satiety, in contrast to both diet and regular soft drinks. It’s thought that the intense sweet flavour may stimulate appetite. Coffee and tea are also reasonable alternatives provided that caloric sweeteners and whiteners are used sparingly.


  1. Panel on Dietary Reference Intakes for Electrolytes and Water. 2005
  2. Jequier E, Constant F. Water as an essential nutrient: the physiological basis of hydration. Eur J Clin Nutr. 2009 Sep 2;
  3. Valtin, H. (2002) “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8”? Am J Physiol Regul Integr Comp Physiol. 283(5):R993-1004 PMID: 12376390
  4. Popkin BM, Barclay DV, Nielsen SJ. Water and food consumption patterns of U.S. adults from 1999 to 2001. Obes Res. 2005;13:2146–2152
  5. Muckelbauer R, Libuda L, Clausen K, Toschke AM, Reinehr T, Kersting M. Promotion and provision of drinking water in schools for overweight prevention: randomized, controlled cluster trial. Pediatrics. 2009;123:e661–667
  6. Stookey JD, Constant F, Gardner CD, Popkin BM. Replacing sweetened caloric beverages with drinking water is associated with lower energy intake. Obesity (Silver Spring) 2007;15:3013–3022.
  7. Dennis EA, Dengo AL, Comber DL, Flack KD, Savla J, Davy KP, Davy BM. Water Consumption Increases Weight Loss During a Hypocaloric Diet Intervention in Middle-aged and Older Adults. Obesity (Silver Spring) 2009 Aug 6
  8. Black RM, Leiter LA, Anderson GH. Consuming aspartame with and without taste: differential effects on appetite and food intake of young adult males. Physiol Behav. 1993;53:459–466.
  9. Almiron-Roig E, Drewnowski A. Hunger, thirst, and energy intakes following consumption of caloric beverages. Physiol Behav. 2003;79:767–773.


Leave a Reply