Preppers: Stay Hydrated!

You’ve probably heard the advice: “drink 8 cups of water a day”. What is the basis for that advice, and is it sound? It turns out that the amount 8 cups/day is based mainly on observational studies. The average adult living in a temperate climate consumes about 2 to 3 liters of fluids (not just water) per day. [1] And 2 liters is just over 8 cups. So the advice is not based on what is healthiest for you or for the average person, but only on the lower end of the usual intake.

Note that this average adult intake of fluids, 2 to 3 L/d, includes all beverages, not just water. Also, in some studies, researchers included water intrinsic to various foods, such as meat, fish, fruits, vegetables, pasta, and soup as part of the daily fluid intake. [2] Drinking 2 to 3 liters/day of just water would be excessive and possibly harmful for some persons, especially when we add the fluids from other beverages and from food. Counting only the fluids found in a wide range of beverages, average intakes for adults are more in the range of 1.1 to 2.2 L/day, which is 5 to 9 cups per day. [3]

Sometimes the advice of 8 cups/day is phrased so as to limit the 8 cups to water, and to exclude soda, sugary drinks, milk, and caffeinated beverages. But a 2010 article at Nutrition Reviews objects to this idea: “There is really no existing information to support an assumption that consumption of water alone or beverages containing water affects hydration differentially.” [4]

An article at says much the same thing:

Everyone has heard the advice, “Drink eight 8-ounce glasses of water a day.” That’s about 1.9 liters, which isn’t that different from the Institute of Medicine recommendations. Although the “8 by 8″ rule isn’t supported by hard evidence, it remains popular because it’s easy to remember. Just keep in mind that the rule should be reframed as: “Drink at least eight 8-ounce glasses of fluid a day,” because all fluids count toward the daily total. [5]

You might need less than 8 cups of fluids per day, or you might need more. Each person’s water needs vary based on level of physical activity, temperature, humidity, body size, and other factors. Just as with total daily calories, a smaller person generally needs less fluids than a larger person. If you are 5 feet zero inches tall with a slight frame, you need fewer daily calories and less fluids. If you are 6 feet 6 inches tall with a large frame, you need more daily calories and more fluids. Then, too, athletes, other persons who are physically active, and anyone outside in the hot sun all day also need more fluids. So the 8 cups/day rule is not particularly useful.

For good health, you need to avoid dehydration and avoid over-hydration. That is the guideline currently supported by studies on this topic. The saying of “8 cups per day” is at best an average adult intake, and at worst a poor fit for many persons.


Can you simply depend on thirst to indicate whether you are getting enough fluids or not? Sometimes, yes; other times, no. In general, adults will get thirsty and will choose to drink fluids, thereby avoiding dehydration. However, in some circumstances, the thirst response might not keep up with fluid loss. It is not unusual for an adult to become dehydrated due to physical activity in hot dry weather. The dehydration occurs more quickly than the usual response of thirst and fluid intake.

Another issue is a decrease in thirst response and in sensitivity to dehydration in elderly persons.

“when challenged by fluid deprivation, a hyperosmotic stimulus [e.g. food that is salty or sugary], or exercise in a warm environment … older adults exhibit decreased thirst sensation and reduced fluid intake. Full fluid restoration eventually occurs, but full restoration of fluid balance is slowed. The aging process alters important physiological control systems associated with thirst and satiety.” [6]

Drinking fluids in response to thirst is an essential part of good health. But for optimum health, you might need to drink some fluids even if you do not feel thirsty. Coffee and diet sodas are acceptable sources of fluid. Milk is healthy in moderation. But green tea is the single beverage with the most support in medical studies for its good effects on health. I would suggest at least 3 cups/day of green tea, along with a few other beverages of your choice. The average adult intake of 5 to 9 cups/day is a good starting point. Increase fluids if you are taller or heavier, are physically very active, or live in a hot or dry environment.

A article has some general advice on remaining safely hydrated:

“Generally if you drink enough fluid so that you rarely feel thirsty and produce 1.5 liters (6.3 cups) or more of colorless or light yellow urine a day, your fluid intake is probably adequate. If you’re concerned about your fluid intake or have health issues, check with your doctor or a registered dietitian. He or she can help you determine the amount of water that’s right for you.” [7]

If your urine has a darker yellow or amber color or you produce little urine, you may be dehydrated. Try increasing fluid intake. If that does not work, consult a physician.

The Mayo Clinic article also suggests drinking one glass of water or low-calorie beverage with each meal and one between each meal. That’s 5 cups of beverages per day: 1 for each of 3 meals and 2 more in-between the meals. You should also drink water before and after exercise, but usually an additional cup or two of fluids is sufficient.


Dehydration can cause serious health problems or death. [8] But the opposite problem, over-hydration caused by excess fluid intake, can also cause harm or death.

The Mayo Clinic website explains:

“Although uncommon, it is possible to drink too much water. When your kidneys are unable to excrete the excess water, the electrolyte (mineral) content of the blood is diluted, resulting in low sodium levels in the blood, a condition called hyponatremia. Endurance athletes, such as marathon runners, who drink large amounts of water, are at higher risk of hyponatremia.” [9]

The medical term “hyponatremia” means “too little sodium”. Excess fluid intake can dilute the electrolytes in the blood, resulting in life-threatening heart arrhythmias and other serious health problems. A person can literally die from excess intake of fluids, especially plain water. Sports drinks like Gatorade and Powerade include some electrolytes, making this problem less likely. But no sports drink has sufficient electrolyte content to be the sole or main source of electrolytes in the diet.

Preppers: stay hydrated!

– Thoreau

[1] Popkin et al., Water, hydration, and health; Nutrition Reviews. Volume 68, Issue 8, pages 439-458, August 2010.
[2] Ibid., Table 4.
[3] Ibid.
[4] Ibid., p. 447.
[5], Healthy Lifestyle, Nutrition and healthy eating, “Water: How much should you drink every day?
[6] Kenney and Chiu, Influence of age on thirst and fluid intake; Medicine and Science in Sports and Exercise. 2001, 33(9):1524-1532.
[7], Healthy Lifestyle, Nutrition and healthy eating, “Water: How much should you drink every day?
[8] WebMD, Information and Resources, “Dehydration in Adults
[9], Healthy Lifestyle, Nutrition and healthy eating, “Water: How much should you drink every day?”

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