How Much Water Should I Drink As I Age? The Science

 

One of the most important health decisions you make every day is “How much water should I drink today?”   Why?  Because properly managed hydration is critical to your well-being – how you feel, how your body cleanses itself, fights disease and deterioration of the body’s cells.

 

I would argue that there is no aspect of your long-term life decisions more critical to your well-being than hydration management - especially as you age.  Aging makes these decisions increasingly more important. 

 

But how to best manage your hydration is not so easy an exercise.  Simplifications and confusing advice abounds.  Even the common “8 glasses a day” recommendations are too simplistic and rigid. 

 

Okay then, how much water should I drink?  What does the science say?

 

I was confused myself as I was embarking on a journey to improve my eating, drinking and exercise choices.  As I say continually in my writings, pursuing an ageless life is more challenging when your physical or mental health are compromised. 

 

Dehydration, obesity and anxiety sap energy and impair focus.  Only conscious, intentional action can enable you to fight your way back onto the path forward toward the life of meaning and fulfillment to which you aspire.

 

I’ve researched leading scientific publications on this confusing topic to see if I could discern a consensus on this not-so-simple question “How much water should I drink?”  Sources I researched include, The Mayo Clinic, The National Institutes Of Health (NIH), Harvard Public Health, WebMD, Healthline, McGill University in Canada, The American Journal Of Physiology, The Journal of Human Nutrition and Dietetics and other respected authorities on health.

 

This research was a bit mind-numbing.  Reading scientific abstracts hurts my eyes and numbs my brain.  I started writing this post organizing and summarizing study results.  But it became clear that the post would be way too long, too intense and would bore you into submission. 

 

So, instead, below are my most important science-based takeaways from my extensive research.  Every detail here is included in the Reference articles at the end of this post (if you have the fortitude to wade through them):

 

1  Not drinking enough water is a serious issue, and is potentially dangerous.

·      

Reduced Cognitive Performance

 

Even mild levels of dehydration can produce disruptions in mood and cognitive functioning - concentration, alertness and short-term memory.  This may be of special concern in the very young, very old, those in hot climates, and those engaging in vigorous exercise. Confusion and delirium in the elderly can often be traced, in part, to low water consumption.

·       

Impaired Physical Performance

 

Exercise can cause a loss of 2-10% in body weight, depending on how strenuous. This level of dehydration can result in reduced endurance, increased fatigue, altered thermoregulatory capability, reduced motivation, and increased perceived effort.  The more strenuous and longer the exercise, and the hotter the conditions in which the exercise is performed, the greater the dehydration and the greater the need for hydration.

 

There is a tendency to underestimate the need for hydration during exercise.  So the more strenuous and longer the exercise, and the hotter the conditions, the more important it is to proactively hydrate even more than you think necessary.  Children are most susceptible to problems because they tend to not recognize hydration needs as well as adults.

·       

Impaired Bodily Functions

 

Reduced kidney function, reduced blood pressure, increased heart rate, constipation, increased headaches

·       

Reduced skin thickness and density

·       

Susceptibility to some chronic diseases – e.g., kidney stones and bronchopulmonary disorders

·      

Increased intensity of hangovers

 

Alcohol induces water loss/dehydration.  To mitigate the effects, drink a glass of water between drinks and have at least one big glass of water before you start drinking and before going to bed.

 

2  Drinking too much water is seldom dangerous. 

 

Unless you are drinking a lot of water at one time, which can cause water intoxication, or you have heart or kidney disease where processing water is impaired, drinking more water than your body needs is not a real problem.

 

In fact, if you consider that your body has inside it about 5 liters of blood, and that your kidneys filter about 180 liters of blood daily, that means your blood is being filtered about 36 times a day.  

 

So adding relatively small amounts of extra water daily is like a drop in the bucket.  It just doesn’t make much of a difference in a relatively healthy person.

 

And since drinking lots of water to flush toxins out of your body to prevent diseases is a myth, there isn’t any good reason to drink more than enough to maintain health.

 

So drinking how much water daily is “enough?”

 

The most common recommendation is (8) 8-ounce glasses a day.  That number derives from a 1945 publication by the US Food and Nutrition Board which recommended 2.5 liters of daily water intake - about (10) 8-ounce glasses. 

 

However, there was no scientific findings backing that recommendation, and the recommendation noted that most of the water could come from food sources.  So, over time, the recommendation synthesized into (8) 8-ounce glasses.  Not very scientific.

 

In fact, virtually all of the scientific papers I researched indicated that a healthy, relatively sedentary individual  who walks a few times a week for exercise and eats a normal diet does not need to drink as much as (8) 8-ounce glasses daily.  It won’t hurt, but it isn’t necessary.  And it won’t prevent disease.

 

But if you exercise strenuously, especially if you exercise or participate in extended athletic endeavors like tennis, soccer, running, etc. where there is more substantial water loss through sweating, additional hydration is necessary.  But that re-hydration need is a short-term replacement.  It doesn’t mean you have to carry a water bottle around all day drinking large amounts of water.

 

The average person normally loses about 1.5 liters of water daily (about (6) 8-ounce glasses) through sweat, breathing and urination.  And, since about 20-30% of water is consumed daily in food, more if the diet is high in fruits and vegetables, (8) 8-ounce glasses of water daily is more than enough for maintaining health.  If you exercise strenuously, add a few glasses of water with electrolytes after the exercise as replacement and you’re good to go.  It’s really that simple.

 

The Water Content Range for Selected Foods:

Percentage	Food Item
100%	Water
90–99%	Fat-free milk, cantaloupe, strawberries, watermelon, lettuce, cabbage, celery, spinach, pickles, squash (cooked)
80–89%	Fruit juice, yogurt, apples, grapes, oranges, carrots, broccoli (cooked), pears, pineapple
70–79%	Bananas, avocados, cottage cheese, ricotta cheese, potato (baked), corn (cooked), shrimp
60–69%	Pasta, legumes, salmon, ice cream, chicken breast
50–59%	Ground beef, hot dogs, feta cheese, tenderloin steak (cooked)
40–49%	Pizza
30–39%	Cheddar cheese, bagels, bread
20–29%	Pepperoni sausage, cake, biscuits
10–19%	Butter, margarine, raisins
1–9%	Walnuts, peanuts (dry roasted), chocolate chip cookies, crackers, cereals, pretzels, taco shells, peanut butter
0%	Oils, sugars

Source: The USDA National Nutrient Database for Standard Reference, Release 21

 

I love watermelon. So in-season, I don’t need that much water at all because the watermelon is 90%+ water and I eat a lot of it.  But I’m a big guy, and water needs are affected by weight.  So I know I need more than normal.

 

Bottom line, your own body normally tells you if you’re not hydrating enough.  You get thirsty.  Your urine darkens and begins to smell.  You feel lethargic.  You may feel a little less clear-headed or dizzy.  If so, just add some more water to your daily intake and see if the symptoms dissipate. 

 

If not, there may be another organic cause and you may need to seek medical advice.  If you have other issues, like heart or kidney problems, advanced age or diarrhea problems, your doctor will advise you.

 

So here’s my overall takeaway after all the somewhat confusing research:

 

The core directive is to drink ENOUGH water to stay healthy – but drinking a lot more doesn’t help.  So based on normal daily water loss and replacement need,  I think (6)to(8) 8-ounce glasses of water, or 48-64 ounces daily, is about right for average weight,  for young to middle age people (juices, sodas, flavored water, even tea and coffee, but not alcohol, count – there are other dietary reasons for limiting sugary drinks). 

 

Since I’m older, since the thirst trigger isn’t as sensitive in older people, since added water doesn’t hurt, and since I minimize my drinking of juices, sodas and do not drink tea or coffee, I try to drink at least 64-72 ounces of water daily (I’m also heavier than normal), spread out over the entire day, and do not count water from food (except when I am eating lots of watermelon). 

 

The little extra water doesn’t hurt, and it makes me feel like I’m being careful at age 77 – since it is dehydration that is the enemy, not too much water.

 

For an average weight person, 48-64 ounces of water, not including from food, should be sufficient.  Your body will tell you if you need more.  Tap water is fine, unless you have some water issues. 

 

We buy gallon jugs of basic water at the grocery store for $1 or sometimes less, keep a gallon jug in the refrigerator and pour it into 16-ounce glasses to drink.  And for electrolytes, I drink Propel and Marianne drinks Electrolyte Water or Smart Water.  We keep it simple.  And we both feel great.

 

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Here are the primary Sources that I reviewed for this post:

 

https://www.health.harvard.edu/blog/big-benefits-plain-water-201605269675

https://pubmed.ncbi.nlm.nih.gov/11022872/

https://www.healthline.com/nutrition/7-health-benefits-of-water

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908954/

https://www.mcgill.ca/oss/article/health-nutrition/water-myth

https://journals.physiology.org/doi/full/10.1152/ajpregu.00365.2002

https://www.webmd.com/diet/features/6-reasons-to-drink-water

https://www.slenderkitchen.com/article/how-to-calculate-how-much-water-you-should-drink-a-day

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4027093/

https://jamanetwork.com/journals/jama/fullarticle/2680548