Hydration Equation

The Hydration Equation

“Water, water, every where, Nor any drop to drink.” From the Rime of the Ancient Mariner (1834), Samuel Taylor Coleridge

You’ve no doubt been told that you are supposed to drink at least eight ounces of water eight times a day (often referred to as 8×8).  The daily race to meet that goal has turned us into a society of water bottle carriers.  In the car, at school and at work, the water bottle is a constant companion, much like a cell phone.  In fact, since 2010 bottled water sales have passed the sales of carbonated soft drinks. Americans consumed 14.4 billion gallons of bottled water in 2019.[1]

We all know that staying hydrated is an important part of being healthy, we are, after all, made up of 60% water.  Water lubricates your joints, and cushions the brain and spinal cord.  It improves blood flow and regulates temperature. The digestive system relies on water to process and move food.  Every cell, tissue and organ relies on water to keep our bodies healthy.

We get hydration from food like fruits and vegetables, and all beverages we consume add to the amount of water in our bodies including coffee, tea, soft drinks and alcohol.  That’s right: Everything you can drink and the juice from a lot of things you can eat all count, metabolically speaking, as good old H2O. So where did this whole drink strictly water until you burst theory start?  That’s an interesting question because there is absolutely no scientific basis for how much water you should consume each day.

In 1974, a nutritionist by the name of Fredrick J. Stare wrote

“How much water each day? This is usually well-regulated by various physiological mechanisms, but for the average adult, somewhere around 6 to 8 glasses per 24 hours and this can be in the form of coffee, tea, milk, soft drinks, beer etc.  Fruits and vegetables are also good sources of water.”[2]

Prior to this statement, there was no scientific research that addressed how much water we should be drinking each day.  In 1978, the US Department of Agriculture published the results of a survey about the drinking habits of over 26,000 people.[3]  This included water, coffee, tea, soft drinks, alcohol, milk and juices – just about every source of hydration that people consume. The results showed that people between the ages of 20 and 64 were consuming just under one half-gallon of liquid each day.  Surprisingly, that amount correlates to about 6 to 8 glasses of liquid.

After twenty years of heeding the advice to drink 8 glasses of water a day, the US Department of Agriculture again completed an extensive survey of water intake.[4]  In 1998 the survey found that the amount of liquid consumed increased to just over one half-gallon of liquid each day. The intake of actual water was increased by about 25%.

There are some studies that indicate drinking plenty of water, in place of other beverages, can help curb diabetes.[5]  Other studies point to water consumption as an aid in weight loss, possibly because there are no calories in water yet drinking water can cause you to feel full.  And staying hydrated helps your heart pump more efficiently, which helps all your organs work better.

Most of the time your body will tell you when you need to drink more fluids because you begin to feel thirsty.  You’ll know you’re getting dehydrated when your mouth feels dry and sticky.  More serious signs of dehydration include dark urine and headaches.

Dehydration can cause physical problems like muscle cramps, dizziness, confusion and even heat stroke. Athletes and people working outside in the heat must be mindful of their fluid intake.  And it bears repeating, if you have diabetes or heart disease you’ll also want to be sure to watch your fluid intake to avoid dehydration.

Older people and young children are also at a higher risk of dehydration.  The older you get the less total body fluid you have so there is less fluid in reserves.  As you age, your thirst response is weakened so you may not know that you are getting dehydrated. Additionally, kidney function declines with age so you will lose more fluids through urination causing you to dehydrate faster.

Children are especially susceptible to dehydration when they are ill because they have less fluid volume in reserves.  Diarrhea, vomiting and fevers all cause fluid levels to decline and in children this happens very quickly.  When playing or participating in sports, be sure to keep children well hydrated for the same reason.

The good news is that, between the convenience of bottled water and the move away from soft drinks, we are all consuming more healthy fluids daily.  Can there be too much of a good thing?

It turns out that you can drink too much water and cause water poisoning.  Too much water can cause the cells in your body to swell and put pressure on blood vessels, your heart and your brain. It’s rare, but if you were to consume too much water, you may suffer from an imbalance in your sodium levels which could cause seizures, coma or death. You would know you’ve had too much if your urine is clear or you are suddenly making frequent (more than 6 to 8) trips to the restroom during the day.

So how much fluid do you really need each day to stay hydrated and healthy? The latest information comes from a report by the National Academies of Science, Engineering and Medicine. The report set general recommendations for fluid intake based on detailed national data.  Women should drink around 2.7 liters or about three-quarters of a gallon and men should drink around 3.7 liters or just about 1 gallon of fluid. It’s interesting to note that, like the comment by Fredrick Stare (above), water comes from all sources.

“We don’t offer any rule of thumb based on how many glasses of water people should drink each day because our hydration needs can be met through a variety of sources in addition to drinking water,” said Lawrence Appel, chair of the panel that wrote the report and professor of medicine, epidemiology, and international health, Johns Hopkins University, Baltimore. “While drinking water is a frequent choice for hydration, people also get water from juice, milk, coffee, tea, soda, fruits, vegetables, and other foods and beverages as well. Moreover, we concluded that on a daily basis, people get adequate amounts of water from normal drinking behavior — consumption of beverages at meals and in other social situations — and by letting their thirst guide them.” [6]

You can easily stay healthy and prevent dehydration by remembering to drink plenty of fluid with meals, before and after exercise and whenever you feel thirsty.


[1] Data Shows Bottled Water Consumption Continues To Increase. Shelby Report. (2020, May 21). https://www.theshelbyreport.com/2020/05/21/bottled-water-consumption-increases/.

[2] Stare, F. J., & McWilliams, M. (1982). In Nutrition for good health: eating less and living longer! (p. 175). essay, G.F. Stickley Co.

[3] United States Department of Agriculture. (1979). (rep.). 1977-78 Nationwide Food Consumption Survey. Springfield, VA.

[4] United States Department of Agriculture. (1979). (rep.). 1994-1996 Continuing Survey of Food Intakes by Individuals (CSFII). Springfield, VA.

[5] Data Shows Bottled Water Consumption Continues To Increase. Shelby Report. (2020, May 21). https://www.theshelbyreport.com/2020/05/21/bottled-water-consumption-increases/.

[6] Institute of Medicine. 2005. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press. https://doi.org/10.17226/10925.

2021-07-20