Water Research Confirms Needs for Healthy Water Consumption
Research from Australia has reviewed the various human studies done over the past 80 years on water consumption requirements. The findings of the study has found that, even with a large variance of study protocols and parameters, the need for considerable water intake is necessary to health.
The research, published in this month’s European Journal of Clinical Nutrition, comes from Dr. A.P Vavanti, Nutrition and Dietetics expert from the Princess Alexandra Hospital in Queensland. Dr. Vavanti and his team reviewed 89 conventional medical studies and papers from peer-reviewed medical research journals that measured and discussed water requirements for humans over the past 80 years.
Dr. Vavanti’s research found that there have been a variety of different techniques employed to measure water requirements, and these resulted in various formulae and calculations to ascertain how much water we really need to drink.
These come from a variety of different protocols, including water-body weight calculations, water-kilocalorie calculations to water-body surface area calculations.
Body surface area calculations for water requirements began in the 1930s because water needs in animals had been extensively studied using the body surface areas of the different animals. Well over 300 animal studies led to a consensus of water requirements in animals using surface area calculations.
This led to humans being referenced using similar calculations, using a proportion of milliliters of water requirement per meter squared (ml/m2) of body surface area. Multiple studies using these calculations arrived at a general consensus of 1500-1600 ml/m2 of water requirement for adults.
As an average adult has between 1.5 and 2 m2 of body surface area, this converts to from about 80 ounces a day for women to about 108 ounces a day for men.
Research has also calculated water requirements by calories burned, using the scientific kilocalorie. This research also began in the 1930s and has continued through the 90s. Initial studies concluded that about one milliliter of water per kcal was the minimal requirement – with the ranges being 1.5ml/kcal to 66 ml/100 kcal. This generalized 1 ml/kcal of minimal water requirement for adults has been supported by the National Research Council.
Children require more water per kilocalorie than adults according to the research, with the consensus being about 1.5 ml/kcal.
Meanwhile a German water consumption study of more than 2,000 adults documented average water consumption at 1.01 ml/kcal for men and 1.06 ml/kcal for women.
However, research that included the loss of water due to sweat and stool – not calculated in some of the early calculations, arrived at a 1989 calculation of 1.5 ml/kcal.
This standardization produces a useable conversion from calorie requirements to water needs. Many consider 2,000 common calories (a common calorie is roughly equivalent to a kcal) a day to be healthy, which would convert to a water need of about 3,000 ml of water per day (101.4 ounces). Active adults, however, can easily burn 2,500 or more calories a day, boosting their water requirements considerably.
These calculations produce some consistency with the surface area calculations.
Note that these water need calculations have determined complete water requirement, not drinking water. Foods also contain water, and several studies have calculated the average water content of a typical diet, ranging from 700 to 1,000 milliliters of water (24 to 34 ounces) from foods.
Water need per body weight has been the most prominently used calculation among the various studies over the past century, especially among the most recent studies. Many of these also included population studies, concluding that a range of 35-45 milliliters per kilogram of body weight was an appropriate water requirement.
This means, for example, that a 150-pound adult would have a water consumption requirement of about 2,380 to 3,060 milliliters of water per day – equating to 80 to 104 ounces.
After we subtract the availability of water from our foods, we arrive at a range of about 60 – 80 ounces of required drinking water or similar fluids per day for the average 150 pound adult.
These different studies and calculations appear to correspond somewhat closely – although a bit short – to the famous six to eight glasses of water a day recommended by so many over recent years. If we assume a glass of water is eight ounces, then six glasses a day would only equate to 48, although eight glasses would equal 64 ounces, which would get a 150-lb adult into the minimal range.
Of course, should the adult weigh more than 150 pounds, drinking more water would be required according to this standard.
Vivanti AP. Origins for the estimations of water requirements in adults. Eur J Clin Nutr. 2012 Dec;66(12):1282-9.
Adams C. Pure Water: The Science of Water, Waves, Water Pollution, Water Treatment, Water Therapy and Water Ecology. Logical Books, 2010.