Goal · Hydration

How much water you need, from drinks and food

Most healthy people meet their water needs by drinking when thirsty and with meals. Older adults, people who are ill and endurance athletes are the exceptions worth planning for.

By the editors of Alimentotherapy Last reviewed October 19, 2026 4 min read Not medical advice

The short answer

The National Academies' reference intake for total water is about 3.7 liters a day for men and 2.7 liters for women, counting all drinks and the water in food, and about 20% of it usually comes from foodNasem 2004. For most healthy people, drinking when thirsty and having beverages with meals covers it; heat, hard exercise and illness raise needs, and older adults are at higher risk of running shortNasem 2004; MedlinePlus.

How much, and from what

The 2004 Institute of Medicine report set its reference amounts from national survey data on people who appeared adequately hydrated: about 2.7 liters (91 ounces) of total water a day for women and 3.7 liters (125 ounces) for men. Those figures cover healthy, sedentary people in temperate climates; very active people in hot weather can need six liters or more Nasem 2004.

"Total water" is the key phrase. About 80% comes from drinking water and other beverages, caffeinated drinks included, and about 20% from food Nasem 2004. Milk, juice, tea, coffee and soup all countMedlinePlus. There is no need to force down eight glasses of plain water on top of everything else.

Water-rich foods

Fruit and vegetables are mostly water: cucumber, lettuce, watermelon, strawberries, oranges and tomatoes are obvious examples, and soups, stews and cooked grains such as oatmeal add more. A diet built around produce supplies a good share of the 20% from food without anyone counting.

Thirst, and when it is not enough

Thirst is a good guide for most people Nasem 2004, but it changes with ageMedlinePlus. Older adults and people with diabetes are at higher risk of dehydration, as is anyone losing fluid through fever, vomiting, diarrhea or heavy sweating, or not drinking because they feel sick MedlinePlus. For an older relative, a drink with every meal and snack and a glass within reach is more reliable than waiting for thirst.

Signs of mild to moderate dehydration are thirst, a dry or sticky mouth, not urinating much, darker yellow urine, headache and muscle cramps. Severe signs include very dark or no urine, dizziness, confusion, a rapid heartbeat and sunken eyes MedlinePlus. Dehydration also dulls attention: in a meta-analysis of 33 studies, attention and executive function were impaired, more so beyond a 2% loss of body weight Wittbrodt 2018.

Electrolytes and illness

For everyday life, water and food cover electrolytes. They matter when you lose a lot of fluid. With dehydration, MedlinePlus suggests sipping water or sucking ice chips, and trying water or sports drinks that contain electrolytes; anyone with fever, vomiting or diarrhea should drink plenty of fluidsMedlinePlus. For vigorous sport, MedlinePlus advises fluids such as sports drinks with electrolytes to keep blood sodium in a healthy range MedlinePlus. Broth (see bone broth) supplies both fluid and salt when you are unwell.

Too much water

Drinking far more than you lose can dilute blood sodium, a condition called hyponatremia. Symptoms include confusion, headache, nausea and vomiting, fatigue, muscle cramps and, in severe cases, seizures, coma and death MedlinePlus. In a study of 488 Boston Marathon runners, 13% finished with hyponatremia and 0.6% with critical levels; gaining weight during the race, a sign of drinking more than was sweated out, was the strongest risk factor along with finishing times over four hoursAlmond 2005. On long events, drink to thirst rather than at every station.

Some conditions, including heart failure, kidney disease and liver disease, upset the body's water and sodium balance MedlinePlus. If you have one, follow the fluid advice from your care team. It may be a limit rather than a target.

When to see a clinician, not the pantry

Signs of severe dehydration: no urine or very dark urine, dizziness or lightheadedness, confusion, a rapid heartbeat or sunken eyes.
Vomiting or diarrhea in a baby, young child or older adult who cannot keep fluids down.
Confusion, headache, nausea or vomiting after drinking large amounts during endurance exercise: this can be low blood sodium and is an emergency.
Constant thirst with frequent urination: a possible sign of diabetes.
You have heart, kidney or liver disease and are unsure how much to drink.

Common questions

How much water should I drink a day?

The National Academies' reference for total water is about 3.7 liters a day for men and 2.7 liters for women, from all drinks and food combined, with about 20% usually coming from food. For most healthy people, drinking when thirsty and with meals is enough; heat and hard exercise raise needs.

Do coffee and tea count toward hydration?

Yes. The National Academies report counts caffeinated beverages toward total water intake, and MedlinePlus lists tea, coffee, milk, juice and soup as sources. About 80% of total water comes from beverages and 20% from food.

Can you drink too much water?

Yes. Drinking far more than you lose can lower blood sodium (hyponatremia), causing confusion, nausea, headache and, in severe cases, seizures. In a study of 488 Boston Marathon runners, 13% finished with hyponatremia, and weight gain during the race was a key risk factor.

Sources

Primary research and government sources, each checked on the date this page was reviewed.