Water Intake: You (and your clients) don’t need as much as you think

Have you ever wondered how your dog has never become dehydrated? I mean, without a lululemon water bottle that has perfectly measured markings so they know *exactly* how much water they’re getting everyday, how can you be sure your dog hasn’t been on the brink of death this whole time?

I’m going to tell you why and it’s not, despite your claims to the contrary, because your dog is smarter than your neighbor’s child.



I had noted that I would do a post like this a few weeks ago when a colleague of mine chided me to get it done because his clients wouldn’t listen to him about fluid intake. Namely, he’s a high-intensity guy who trains clients in a controlled environment (~65* F, humidity controlled), but his clients are probably wearing tennis skirts and drinking water like they’re crossing the Sahara. So let’s start there.

Water Recommendations

Have you ever wondered why 8 glasses of 8 ounces of water per day has been recommended? Well, the truth is that there’s not good evidence for this claim as a concept, as evidenced by a research review published in the Journal of the American Society of Nephrology. Researchers concluded “There is no clear evidence of benefit from drinking increased amounts of water.” The notion of consuming 64oz of water per day dates back to the 1945, where what is now the Institute of Medicine recommended drinking once milliliter of water per calorie of food consumed. Based on average consumption estimations at the time, this worked out to almost 64oz of water per day. The problem was that they didn’t account for the fact that food gives you tons of water and counts toward your water intake. Take a look:

Water Balance

You’ll notice in the diagram above that water intake from food accounts for nearly as much water as water from fluid intake. So if you’re getting adequate nutrition, you’re getting a lot of water. How do you make up the water differences in your daily life? You get thirsty and, despite what you’ve heard, thirst does not mean you’re already dehydrated. On the contrary, thirst begins when the concentration of blood (an accurate indicator of our state of hydration, because remember blood is filled with other things) has risen by less than two percent, whereas most experts would define dehydration as beginning when that concentration has risen by at least five percent.

This is why your dog isn’t dead in the backyard after trying to get that squirrel obsessively and why you, despite years of never paying attention to your hydration status before you started exercising, are reading this. Drink when you’re thirsty and you’re covered.

Fluid during exercise

Exercise is a slightly different animal. Take a look at the diagram above and you’ll see significant increases in fluid output in the form of sweat. This is because sweating is our main mechanism of cooling, as evaporation of the sweat is wickedly efficient at keeping us from dying. This is important because the human organism handles drops is body temperature far better than it handles increases in body temperature. So not only are you sweating like a pig, but you’re breathing more heavily, which forces more water out of you as vapor, further cooling your body.

Under these circumstances, more water is necessary, but not as much as you think. In fact, too much water with all of that sweating leads to a condition called hyponatremia, which is where the blood is diluted to the point where electrolyte concentration falls to the point where the normal osmotic balance at the brain is altered. As a result the brain swells and you could end up with fun outcomes like death. Another name for this? “Water Intoxication.” It’s basically why “oral rehydration” products like Gatorade were invented.

But this is if you’re sweating like a pig in an environment that is hot and humid…basically worst case scenario stuff. What if you’re training in one of our studios? If you’re in my studio, you might not sweat at all as I keep fans blowing and the temperature at 67* F. If you train at Rosedale, it’s likely to be higher but not hot room yoga levels. So if we account for water loss through vapor, which is about 3-4 mL per minute given our example, then you’d exhale 90 to 120 mL of water during a half our session that needs replacing. That’s 3 to 4 ounces, folks. Paltry stuff. If you doubled that 8 ounces, you’d likely account for most of the sweat lost during that time given controlled conditions. Drink to thirst the rest of the day; your body is smarter than you.


  1. Your body is smarter than you and thirst is an accurate indicator of water demands.
  2. During strenuous activity in the heat where intense sweating is occuring, a fluid intake of up to 250mL (~8 ounces) every 15 minutes is recommended, but not more than 1000mL. At that point, an oral rehydration supplement would be appropriate.
  3. If you’re training at Efficient Exercise, or in any other climate controlled environment, much less water, to the tune of 8 ounces per 30 minutes, is appropriate.

251505_10151024760092405_1633409149_nSkyler Tanner is an Efficient Exercise Master Trainer and holds his MS in Exercise Science.  He enjoys teaching others about the power of proper exercise and how it positively affects functional mobility and the biomarkers of aging.



2 Responses

  1. Glynis says:

    This was a very interesting read. As someone who has always had to watch her food and liquid intake, it was eye-opening to read that the standard 8 drinks a day is not necessarily the way to go.
    We are often coerced into believing certain “facts” and left feeling guilty if we don’t meet the standards or rules. Thanks.

  2. Tom says:

    Thanks for that. I have read the 8 glasses comment many times and wondered where it came from. Your guidance on water intake makes a lot more sense to me.

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