Should You Drink 8 Glasses of Water Every Day?

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How Much Water Should You Drink Every Day?

I encounter many patients who adhere religiously to the dictum that they should drink 8 glasses of water a day. But is this really how much water you should be drinking on a daily basis?

3 Points

1. In nearly everyone, our body is programmed to take in adequate fluid. Our thirst mechanism doesn’t allow us to become dehydrated. Unless we ignore our thirst we won’t get dehydrated
2. However, in certain conditions, yes, 8 glasses a day is a good idea.
3. Otherwise, 8 glasses a day has disadvantages and can actually be dangerous.

#1. How Our Body is Programmed

Our thirst mechanism guides us very well as to our need to take in more fluid. Further, if we are behind on fluids, our kidneys reduce the output of urine which helps us preserve body water. When we are ill and our fluid consumption is reduced, or when we are febrile, yes we do need to be encouraged to take in adequate fluid. But when we are well, we can trust our bodies.

#2. Certain Conditions

There are conditions for which we need to increase our fluid intake.

• Kidney stones. If you’ve had kidney stones, increasing your fluid intake is an important measure in trying to prevent recurrent stones.
• Recurrent urinary infections. Here, the increased fluid intake increases urine volume and the frequency with which you will empty your bladder. It shortens the time that any bacteria will sit in your bladder.
• Hot climate or vigorous exercise. Here the thirst mechanism will almost compel us to increase our intake of fluid. But even here, drinking excessive water can be dangerous.

#3. Disadvantages & Potential Dangers

Yes, drinking excessive fluid can be harmful. Here are two common ways they harm us:

First, by increasing the urine volume, we have to urinate more frequently. This means interrupting sleep 2, 3, or more times a night to urinate. This interruption of sleep can be particularly problematic if you have trouble falling back asleep. And, again, you are gaining nothing from it.

Second, in anyone, but particularly in women over the age of 70, excessive intake of water can lead to a condition called hyponatremia, where the concentration of sodium in the blood falls below normal. Patients who are taking a diuretic or certain other medications such as some types of antidepressants (e.g. SSRIs such as Lexapro) also are at increased risk of developing hyponatremia.

Hyponatremia results from the loss of sodium amid a large quantity of urine. A fall in blood sodium concentration can result in fatigue, nausea, confusion, and even seizures and coma. The normal blood sodium level is 135-145. If it falls below 130 or so, symptoms can appear. A fall to below 125 or 120 can be dangerous.

I encounter many patients who drink too much water.

My Advice

My advice is very simple: when you are thirsty, drink as much water as you want. And when you are active and sweating profusely, of course, take in extra fluid, whether before, during, or after. Just eliminate the water you are drinking because you “think it is good for you.”

One other caveat: many individuals drink excessive water because of chronic nasal congestion or because of medications that cause a dry mouth. If so, get treatment for your nasal congestion. Hopefully avoid, if it is possible, long-term treatment with medications that cause a dry mouth.

The Value of the “N-of-1” Experiment in Medical Practice

Guidelines are based on large trials that document that a medication or treatment confers benefit that is statistically significant, and that assess the risk of adverse effects.  The large trials are essential and valuable in enabling physicians to prescribe medications with confidence.

The exact opposite of a large trial would be an “N-of-1” experiment, testing an intervention in an individual patient. The N-of-1 experiment is a crucial component of the clinical management of patients. It is the procedure by which a physician tells a patient – the recommended drug didn’t help, but I think drug X might work very well.

Let’s do the experiment and try it. If it doesn’t help, we can stop it.

About Samuel J. Mann, M.D.

Dr. Mann is a physician, researcher, author, and specialist in the management of hypertension. He focuses his career on improving the management of hypertension by getting patients onto the drugs, combinations, and dosages, that is right for them. Dr. Mann is the author of two books. “Hypertension and You: Old Drugs, New Drugs and the Right Drugs for Your High Blood Pressure” and “Healing Hypertension: A Revolutionary New Approach”. His upcoming book, A Radical New Understanding of the Mind/Body Connection, will be upcoming in 2021. Dr. Mann currently holds the position of Professor of Clinical Medicine in the division of Nephrology and Hypertension at New York Presbyterian – Weill Cornell Center, New York, NY. He has also written extensively about “mind/body” hypertension, offering a very different view of the link between emotions and hypertension, and has pioneered new approaches to treatment.

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