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How much water is enough water?

Elizabeth Jaggers, M.D., is a Piedmont internal medicine physician. In her Short Answer/Long Answer series, she tackles your medical questions.  

Short answer:

There is no formal recommendation for a daily amount of water that people “need,” as this greatly varies based on size, age, daily activities, climate, and co-existing health conditions. The body gets water from consumption of food, water, and non-water beverages. Our kidneys, hormones, brain, and vascular system do an amazing job of regulating water and electrolyte levels and will send signals (a.k.a. thirst) to help maintain this. Unless instructed otherwise by your physician, drink water when you are thirsty and remember that your need for water increases when you are in a hot climate, sweating, and/or exerting yourself.

Long Answer:

“For whatever we lose (like a you or a me), It's always our self we find in the sea.” 

                                                                                      -E.E. Cummings

Our bodies are about 60% water, and water is key to nearly all essential human functions. Among other things, water assists with transportation in and out of our cells, helps us maintain vascular volume (a.k.a. blood), cushions our joints, and plays a role in temperature regulation.

Our bodies have many markers, signals, and sensors in place to regulate this important substance. The one marker we can easily follow is called Osmolality. In this sense, Osmolality refers to the concentration of dissolved particles (sodium, potassium, etc.) in your blood.

When the Osmolality increases by as little as 2% (think of your blood becoming dense and salty), a part of your brain called the hypothalamus sends out the thirst signal. Thirst then motivates us to seek and consume water. Whether you realize it or not, your body is using positive reinforcement – that is why a glass of water tastes SO MUCH BETTER when you are thirsty than when you are not.  

The common hydration advice for years has been “8 ounces of water, 8 times a day.” No one seems exactly sure where the idea of 8 glasses of water a day came from originally, but there has NEVER been a study that validates this. For the average person, this amount of water seems to be a bit of an overestimation.

The question of how much water you should drink a day is a bit contentious. According to the National Academy of Science, Engineering and Medicine: “The vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide.” The Academy goes on to say that general recommendations for women would be 91 ounces and for men 125 ounces of total “water” – but this is including water from food and non-water beverages (including alcohol and caffeinated beverages).

About 20% of our water consumption actually comes from food (especially fruit and vegetables) and non-water beverages like juice, tea, and coffee. Contrary to popular belief, drinking caffeinated beverages like coffee and tea in moderation does NOT have a negative effect on your hydration status.

One thing that everyone agrees on is that staying properly hydrated allows our bodies to function the way they were designed. There is also some research showing improved athletic training performance, mood, and concentration in hydrated people when compared to those who are dehydrated.

Caveat: Those who are prone to having “fluid overload” in their bodies (such as people suffering from liver disease, heart disease, and kidney disease – and especially anyone on hemodialysis) often have to restrict how much water they consume. Also, pregnant women and children may have increased water requirements. As always, if in doubt, verify with your doctor.

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