Water intake
Water is a vital nutrient, making up approximately 60-80% of human cells and tissues. Water plays a foundational role in cellular function, mental and physical performance and our overall health.
Cells and Water
Water is key to maintaining healthy cellular function, including the buildup and breakdown of cellular components, chemical reactions, and protein structure and function, and it acts as a solvent (dissolving agent) and can even function as an antioxidant — protecting cells from damage by free radicals.
Optimize Hydration
Dehydration (even mild dehydration) negatively impacts physical performance, alertness and cognitive focus, and thereby can cause “brain fog.” To ensure proper hydration, aim to consume 8 oz (237 mL) of fluid per hour for the first 10 hours of your day. Note: these are averages! You do not need to neurotically consume 8 oz every hour but rather 16 oz on waking, then 8 oz a few hours later, 32 oz later, 4 oz, etc. Eighty ounces in the first 10 hours of your day, spread out as is practical, is just fine. The issue is simply that most people do not drink enough water volume in the waking hours of their day. Drinking ~80 oz in the first 10 hours after waking can help most people offset dehydration.
Why the first 10 hours? The body’s circadian clock (i.e., sleep and wakefulness pattern) strongly regulates the cells within the kidney and gut via the hormone vasopressin. Within the first 10 hours after waking, the kidney works efficiently to filter fluid, then output reduces (so hopefully, you do not frequently wake up during the night to urinate!). Yes, drinking more water in the daytime will have you going to the restroom more often, but that is not a bad thing.
Exercise, Heat and Hydration
Above meeting your baseline hydration requirements (80 oz/10 hrs of waking), other factors such as exercise, sweating, excess heat, dry environments and caffeine intake affect your hydration requirements. When exercising, follow the Galpin Equation as a guideline for the amount of additional fluid you should consume (again, on average — no need to be neurotically obsessed with consuming exact amounts at exact times during exercise, unless you prefer to.
The Galpin Equation
- Body weight (in lbs.) divided by 30 = number of ounces to consume every 15-20 minutes
- Body weight (in kg.) × 2 = number of mL to consume every 15-20 minutes
If you are in hot temperatures or sweating, increase the Galpin Equation guidelines by an additional 50-100%. For every 20-30 minutes in the sauna, consume an extra 8-16 oz of fluid.
Also, be mindful of how caffeine consumption increases your overall water intake needs, as it is a diuretic. If you drink caffeine, increase fluid intake (ideally with electrolytes like sodium, potassium and magnesium) by 2:1 to offset dehydration. In other words, if you drink an 8-ounce coffee with caffeine, ingest 16 oz of water, ideally with low/no-sugar electrolytes like LMNT, or simply a pinch of salt.
Thirst is a good indicator that you are not sufficiently hydrated, but your perception of thirst lags behind the body’s true hydration status. So not being thirsty does not mean you don’t need more fluid. Therefore, preemptively plan your hydration strategy, especially in extreme weather or high-intensity activities.
How Much Water should I drink each day?
13 cups * 8 oz = 104 oz
104 oz = 3.07565 litre
104 oz = 0.81250077265625 US gallon
Aim for between 2.5 and 3.5 liters (84.5 and 101.4 ounces) of water per day, more if you work out.
References
- https://www.hubermanlab.com/newsletter/optimize-your-water-quality-and-intake-for-health
- https://www.hsph.harvard.edu/nutritionsource/water/