What Andrew Huberman Says About Staying Hydrated: The Galpin Equation, Daily Intake, and What Most People Get Wrong

If you have spent any time on health-and-performance podcasts in the last three years, you have heard Stanford neuroscientist Andrew Huberman‘s voice. His Huberman Lab show is one of the most-listened-to science podcasts in the world, and one of his most-shared episodes is the 2023 deep-dive titled How to Optimize Your Water Quality & Intake for Health. In it, Huberman and his frequent collaborator Dr. Andy Galpin lay out a surprisingly specific set of rules for daily hydration that most adults are not following.

This post unpacks what Huberman actually recommends — the daily-intake formula, the famous Galpin Equation for exercise, the role of electrolytes, what to do in heat — and where his guidance lines up (and doesn’t) with the kind of distilled water Puretap has been delivering across the GTA for over forty years.

Why Hydration Matters More Than People Think

The body is roughly 60% water by mass, and the brain is closer to 75%. Even small drops in hydration status — losses of 1–2% of body weight from sweat — measurably impair cognition, mood, attention, and physical output. Huberman opens the episode by pointing out that hydration is one of the very few interventions that improves both mental and physical performance simultaneously, immediately, and at essentially zero cost.

The mechanism is not mysterious. Water is the medium in which every chemical reaction in your body takes place. It carries nutrients into cells, removes waste, regulates body temperature through sweat, lubricates joints, and maintains the blood volume your cardiovascular system needs to deliver oxygen. When you are dehydrated, every one of those processes runs less efficiently — and your brain notices first.

Huberman’s Daily Intake Rule: 8 Ounces an Hour

Most people have heard the “eight glasses a day” guideline. Huberman’s recommendation is more specific and more useful: about 8 oz (240 ml) of fluid every hour for the first 10 hours of your day, dropping to roughly 5 oz per hour later in the evening to avoid waking up to use the bathroom.

That works out to roughly 80 oz, or about 2.4 litres, of fluid intake during the daytime. For a typical adult that is meaningfully more than the “glass with each meal” routine many people default to. The pacing matters as much as the volume — your kidneys process incoming fluid most efficiently when it arrives in steady amounts rather than in two or three large boluses.

Huberman is careful to note that fluid intake includes water from food (fruits, vegetables, soups), tea, coffee, and other unsweetened drinks. Caffeinated beverages do count toward total fluid intake — the “coffee dehydrates you” idea has been overstated by years of repetition. Caffeine is a mild diuretic, but the water in the coffee more than compensates for the modest extra urine output it triggers.

The Galpin Equation: Hydration During Exercise

The single most-shared formula from the episode is what Huberman calls the Galpin Equation, named for Dr. Andy Galpin, the human-performance scientist Huberman frequently hosts. The rule is simple enough to do in your head:

• Body weight in pounds ÷ 30 = ounces of water per 15 minutes of exertion.
• Or, in metric: about 2 ml of water per kg of body weight every 15–20 minutes.

So a 180-pound (82 kg) athlete should aim for roughly 6 oz (~180 ml) of water every 15 minutes during sustained exercise. A 130-pound (59 kg) runner should aim for closer to 4.3 oz (~130 ml) in the same window. The point is not to hit it on the dot every quarter-hour — Huberman explicitly says “on average, not necessarily on the 1/4 hour” — but to use the formula as a steady target across a workout.

For Galpin’s baseline daily floor, there is an even simpler back-of-envelope rule: drink half your body weight in pounds, in ounces of water, per day. A 160-pound adult, then, would aim for at least 80 oz of fluid daily — almost exactly the same number Huberman’s hourly rule produces. The two heuristics converge on roughly 2.5 litres a day for a typical adult.

When to Drink More: Heat, Sweat, and Sauna

Huberman is clear that the Galpin Equation is a baseline, not a ceiling. If you are exercising in hot weather, sitting in a sauna, or sweating heavily for any reason, he recommends increasing intake by 50% to 100% over the standard formula. Someone who would normally drink 6 oz every 15 minutes during a moderate workout might need 9–12 oz every 15 minutes during a hot summer run.

This is also where the conversation pivots from water alone to electrolytes. Sweat is not pure water; it carries sodium, potassium, magnesium, and chloride out of the body. If you replace heavy sweat losses with water alone, you can dilute your blood sodium concentration faster than the kidneys can adjust — a state called hyponatremia. In its mild form it produces headache and nausea; in its severe form (rare, mostly in endurance athletes) it can be life-threatening.

The fix is straightforward: if you are sweating heavily, drinking large volumes of water, or both, add electrolytes. Huberman recommends adding electrolytes whenever you are exercising hard, sweating in heat, or consuming a lot of caffeine. There are dozens of reasonable products on the market — the brand matters less than the habit.

Hydration for Cognitive Work, Not Just Workouts

One of the more interesting points Huberman makes is that the Galpin Equation should be applied to demanding mental work as well as physical work. Concentrated cognitive effort — coding, writing, deep reading, surgery, even prolonged Zoom meetings — produces measurable increases in metabolic rate and a real drop in hydration status over the course of a few hours. The brain is the body’s most water-intensive organ, and it suffers first when supply runs short.

The practical implication: if you have a long deep-work session ahead of you, treat it the way you would treat a long workout. Have a litre of water on the desk. Add electrolytes if you are also drinking coffee. Don’t wait until you feel thirsty — by the time the thirst signal arrives, you are already 1–2% dehydrated and your performance has already dropped.

Water Quality: Where Huberman Lands, and Where Distillation Fits

The episode is titled “Water Quality & Intake,” and it is worth being honest about the quality side. Huberman’s primary concerns about North American tap water are dissolved contaminants — fluoride, hormone disruptors, pesticide residues, lead from older pipes, and disinfection by-products from chlorine treatment. He recommends filtering tap water with a system that removes those contaminants.

For everyday drinking, the Huberman recommendation — well-filtered tap that retains calcium and magnesium, plus a steady electrolyte habit during exertion — is sound advice for most people. The right way to think about distilled water is as a specialized tool that earns its place in specific contexts, not as a one-size-fits-all daily beverage.

A Practical Daily Hydration Plan, Huberman-Style

• Morning to early afternoon: 8 oz (240 ml) of water per hour for your first 10 waking hours. A 1-litre bottle refilled twice will get you most of the way there.
• During exercise: body weight ÷ 30 = oz per 15 minutes of effort. Increase by 50–100% in heat or heavy sweat.
• Add electrolytes when you are sweating hard, in a sauna, or pairing your hydration with significant caffeine intake.
• Slow down in the evening: ~5 oz per hour after dinner so you sleep through the night without bathroom trips.
• For demanding mental work, treat it like exercise. Have water on the desk. Add electrolytes if the session is long and caffeinated.
• For specific uses — CPAP, supplement mixing, medical applications, or anywhere you want a mineral-free baseline — keep distilled water on hand.

Where Puretap Fits

Most of what Huberman recommends is independent of brand or supplier — drink more water, drink it on a schedule, add electrolytes when you sweat, filter your tap. Where Puretap fits is the specialized end of his framework: when you need genuinely mineral-free, contaminant-free water for a specific purpose, distilled is the cleanest possible base.

Our Morning Mist 1-gallon distilled water is made in Canada in food-grade virgin HDPE bottles, with a milk-jug-style handle that makes refilling a CPAP humidifier or a 1-litre electrolyte bottle straightforward. We deliver across Mississauga and the Greater Toronto Area on a standing-order schedule that suits households, gyms, clinics, and pharmacies. Contact Puretap to set up delivery, or browse our distilled water options online.

Sources

• Huberman, A. (2023). How to Optimize Your Water Quality & Intake for Health. Huberman Lab Podcast, Episode 102. Episode page | Newsletter summary
• Huberman, A. (2023). Twitter/X post on the Galpin Equation: “The Galpin Equation = bodyweight in pounds divided by 30 = the number of ounces of water to ingest per 15 min of exertion.”
• Galpin, A. (host) & Huberman, A. Huberman Lab Guest Series with Dr. Andy Galpin. Hydration discussion across multiple episodes.
• Adan, A. (2012). Cognitive performance and dehydration. Journal of the American College of Nutrition, 31(2), 71–78. (Background reference on the cognitive cost of mild dehydration.)
• Photography: free-licence stock images from Pexels.