Daily Water Intake Calculator
Built on the National Academies' adequate intake figures rather than the bodyweight rule that gets repeated everywhere without a source.
The National Academies publish adequate intake by sex. It's a population average, not a personal prescription.
Each serving needs at least 12 oz of its own, stirred and drunk right away.
Where the number comes from
| Component | Ounces | Basis |
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Nothing you enter here is stored or sent anywhere. The calculation runs entirely in your browser.
Talk to your provider before setting a fluid target if you:
- Have heart failure, kidney disease, or liver disease — several conditions call for fluid restriction rather than more
- Take diuretics, lithium, or other medications affected by fluid balance
- Have been told to limit fluids for any reason
- Are experiencing vomiting or diarrhea and can't keep fluids down
The rule you've seen everywhere isn't from anywhere.
"Drink half your body weight in ounces" gets repeated constantly and doesn't trace back to any authoritative source. The figures this calculator uses come from the National Academies' 2004 Dietary Reference Intakes report: about 3.7 litres of total water a day for men and 2.7 litres for women, counting everything you eat and drink. Roughly 20% arrives through food, which is why the beverage number here is lower than the headline figure.
That same report is titled, in part, Let Thirst Be Your Guide — for most healthy people, thirst works.
These are population adequate intakes, not personal requirements. Body size, medication, and health conditions all shift them.
Spread it out. Large volumes at once sit poorly when gastric emptying is slowed.
Common Questions
How much water should I drink on a GLP-1?
Start from the adequate intake figures above, then add about 12 oz for each psyllium serving you take. The bigger practical issue on a GLP-1 isn't the total — it's spacing it out so it doesn't sit in a slowly emptying stomach.
Does drinking more water fix constipation?
Not by itself. Most of what you drink is absorbed before it reaches the colon. Water matters as the partner to fiber, and osmotic magnesium works by pulling water into the intestine directly. That's the difference between the three levers — see the science page.
Can too much water make nausea worse?
Large volumes at once can, since these medications slow gastric emptying by design. Smaller amounts spread through the day are generally tolerated better.
Do coffee and tea count?
The National Academies figures count total water from all beverages, caffeinated ones included.
Sources
- Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Institute of Medicine / National Academies, 2004 — adequate intake 3.7 L/day (men), 2.7 L/day (women) total water; approximately 20% from food. National Academies.
- Psyllium husk powder labeling — minimum 12 oz of liquid per serving, stirred and consumed immediately. DailyMed, U.S. National Library of Medicine.
- Gastrointestinal adverse effects of GLP-1 receptor agonists and their management, including hydration measures. Gorgojo-Martínez et al., J Clin Med 2022. PMID 36614945.
Staying regular on a GLP-1: my simple daily routine.
Get my free guide — the three levers that work, and the mistakes I see people make.