How Much Water a Day? What NHANES Says Americans Actually Drink
Updated: 1 day ago
"Drink eight glasses a day" is the advice everyone has heard and almost nobody has checked. The useful question is different: how much water do Americans actually drink, and how far is that from what the experts recommend?
The federal government has measured this. We took the numbers and did the subtraction.
The two data sets
The first is the CDC's National Center for Health Statistics data brief on daily water intake among US men and women, 2009 to 2012. It uses NHANES, the national survey in which people report everything they ate and drank over 24 hours. Importantly, it counts total water: plain water plus the water in coffee, milk, soup, fruit and every other food and drink.
The second is the Institute of Medicine's 2004 adequate intake for total water, which the same CDC brief cites: 3.7 liters (125 ounces) a day for men and 2.7 liters (91 ounces) for women.
What adults actually drink
From the CDC brief, mean total water intake per day:
Men, all ages: 3.46 liters (117 ounces)
Women, all ages: 2.75 liters (93 ounces)
Men aged 20 to 39: 3.61 liters
Men aged 40 to 59: 3.63 liters
Men aged 60 and over: 2.92 liters
Women aged 20 to 39: 2.78 liters
Women aged 40 to 59: 2.90 liters
Women aged 60 and over: 2.51 liters
Men with low physical activity: 3.15 liters; high activity: 3.63 liters
Women with low physical activity: 2.55 liters; high activity: 2.98 liters
The brief also reports that only 30 percent of men's total water and 34 percent of women's came from plain water. The rest came from other drinks and from food.
The gap, in glasses
Our method: subtract each group's mean intake from the adequate intake for its sex, then convert the difference to standard 8-ounce glasses (one glass is 0.237 liters). A positive number means the group is short. All inputs are from the CDC brief; the arithmetic is ours.
Men overall: 0.24 liters short, about 1.0 glass a day.
Women overall: 0.05 liters over the target. On average, women meet it.
Men aged 60 and over: 0.78 liters short, about 3.3 glasses a day. This is the largest gap of any group.
Women aged 60 and over: 0.19 liters short, about 0.8 of a glass.
Non-Hispanic Black men: 0.78 liters short, 3.3 glasses. Non-Hispanic Black women: 0.29 liters short, 1.2 glasses.
Hispanic men: 0.37 liters short, 1.6 glasses. Hispanic women: 0.12 liters short, 0.5 of a glass.
Men with low physical activity: 0.55 liters short, 2.3 glasses. Women with low activity: 0.15 liters short, 0.6 of a glass.
Men with high physical activity: 0.07 liters short, a third of a glass. Women with high activity: 0.28 liters over.
The headline is that the average American adult is close to the target. The average hides the people who are not. Men over 60 and men who are mostly sedentary are missing two to three glasses every day, and the brief shows intake dropping rather than rising after age 60.
How much of that is plain water
Apply the plain-water shares to the totals and you get the amount of actual water people drink from a glass or bottle:
Men: 30 percent of 3.46 liters is 1.04 liters, about 4.4 glasses a day.
Women: 34 percent of 2.75 liters is 0.94 liters, about 4.0 glasses a day.
So the typical adult drinks roughly four glasses of plain water, not eight. A more recent CDC summary of NHANES 2015 to 2018 puts adult plain water at 44 ounces a day, about 5.5 glasses. The two cycles used different analyses, so treat the trend as suggestive, but both land well under eight.
So is eight glasses right?
Eight 8-ounce glasses is 1.89 liters. That is 51 percent of the male adequate intake and 70 percent of the female one. Since roughly two thirds of total water already arrives through food and other beverages, eight glasses of plain water would push most people comfortably past the target, and four glasses leaves the average man slightly under it.
That makes "eight glasses" a reasonable round number for a goal, and it is why eight is the default most people pick when Water Textapp asks for a daily goal. If you are over 60 or sit most of the day, the data above says you have the most ground to make up, and a goal of eight glasses closes a three-glass gap with room to spare.
A few caveats the CDC brief itself makes. NHANES intake is self-reported from a single day. Adequate intake is a population guideline, not a prescription for any one person, and needs rise with heat, exercise and some medical conditions. If you have a condition that affects fluid balance, your clinician's number beats any table.
What to do with the number
Pick a plain-water goal in glasses. Eight is a fine default; six is still above the national average.
Count what you actually drink for a week before you judge yourself. Most people overestimate.
Spread it across the day. A gap of one to three glasses is easy to close by lunchtime if you notice it early.
Try it by text
Water Textapp turns the counting into a one-character text. Text Hi to (646) 640-0771, set a goal in glasses, then text a number each time you drink. It replies with your total and what is left, and if you have not hit the goal by late morning or mid-afternoon it checks in. It works on any phone that can text, with no app to install. Your first 20 messages are free, and after that one $9.99 a month subscription covers every Textapp. Details at textapp.co/apps/water.
Comments