Daily Water Requirement

How Much Water do You Need
How much water should you drink each day? What is the daily hydration requirement for an adult? How many glasses of water are needed to be healthy?  We all have asked one form or another of these questions.  How much water does our body need?  There is no one answer for everyone.  Location such as a hot climate, age, weight, activity, and the types of food you eat and drink all influence the answer. Studies indicate that daily water turnover is 3.3 liters for sedentary men and 4.5 liters for active men. For more active adults, particularly those living in a warm environment, daily water need can increase to about 6 liters.


Water Studies and WWII
In 1945, the Food and Nutrition Board of the National Research Council had advised: "A suitable allowance of water for adults is 2.5 liters daily in most instances. An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods." It could be that the last sentence may not have been heeded, and the recommendation was therefore interpreted as eight glasses of water to be drunk each day. (1 glass/cup - approx. 8 ounces = 240ml; therefore 8 glasses = approx. 1920ml).


This is believed to be the source of the misinformation that you should drink 6-8 glasses a day, it ignored the advise that the requirement should be calculated with caloric intake.

The World Health Organization states that "the 'absolute minimum' quantity of water to sustain hydration remains elusive, as this is dependent on climate, activity level and diet".  WHO recommendations for daily requirements of drinking water are men 2.9 liters and for women 2.2 liters.


The advice from the British Dietetic Association is: "In a moderate climate like ours, most of us need around 6-8 glasses of fluid a day; for example, water, milk, fruit juice, tea or coffee, to keep the balance right. However, if we have sweated a lot, because it's hot or we've been exercising, our requirements increase; a good guide is to have an extra one liter of water for every hour of strenuous exercise."


Water Loss
Water is lost from the body as urine, in feces and by evaporation from the skin and lungs (the latter two make up what is called "insensible water loss"). More water is lost from the skin and lungs in high temperatures, at high altitude and when the air is dry. Even in the absence of visible perspiration, approximately half of water loss occurs through the lungs and skin. Water loss through the skin is usually about 800-1000ml per day. In a hot climate, water loss of 500ml per hour is not unusual, but sweating rates can be as high as 2500ml per hour. Expired air is saturated with water vapor and the average water loss from this source is about 300ml per day - this figure may increase if the air is very dry, or during hyperventilation. Urine output can range from 1-2 litres per day, but can be more when large volumes of fluid are consumed. Varying urine output is the main method by which the body regulates net water balance in response to a wide range of fluid intakes and losses.


Daily Water Needed Requirements
So does this lead to an answer?  Yes.  For a general temperate climate for a normally active healthy person (no exercise) in the age range of 19-50 you need an approx amount of fluid around 2600ml or 2.6 Liters.  Assuming 1100ml comes from your food and your body will further metabolize another 250ml from the nutrients and materials, you need app. 1.25 liters (1250ml) a day in the form of drinks.  If you are outside of these ranges (in hot climate or doing more work and/or exercise you need generally another 1-3 liters).


If you are juicing all your foods, your answer is the easiest to calculate.  Measure the amount of your daily juices and then supplement water or beverages until your total liquids equals a minimum of 2.5 liters (2500ml) and then allow a reasonable additional amount (0-3 liters) based upon your level of activity, exercise or climate.  1 cup (8oz.) is equal to 240ml.  

Since water is vital to many functions in the body, including maintaining cell structure, forming a solvent within which chemical reactions in the body can take place, physically transporting other nutrients and oxygen through the body via the bloodstream, transporting white blood cells to fight infection via the lymphatic system, and enabling the body to get rid of waste products via the excretory systems, such as through the formation of urine, I would recommend the overall daily minimum at 3.5 liters.  This would mean that you would consume about 12 cups (96oz. or 2.8 liters) of additional water/fluids as a minimum.