Fluid Intake and Kidney Health: How Much Water You Need

Most healthy adults need about 2.7 liters (91 ounces) of total water a day for women and about 3.7 liters (125 ounces) for men, counting water from all drinks and foods, according to the National Academies. Healthy kidneys adjust how much water you keep or release, so for most people thirst and drinks with meals are enough. People with reduced kidney function are different: their fluid target is set individually by their kidney care team, and it can be lower than these general amounts.

Key Takeaways

The National Academies' adequate intake for total water is about 2.7 L a day for women and 3.7 L for men, from beverages and food combined.
About 80% of total water comes from drinks, including caffeinated drinks, and about 20% from food.
Your kidneys filter about 150 quarts of blood a day and return most of that water to your body; only 1 to 2 quarts become urine.
Some people receive personal limits for fluid, sodium, potassium and phosphorus from their nephrology team. Those limits take priority over any general guideline.
Follow the fluid plan your kidney care team gives you, and get clinician approval before taking potassium, magnesium or any other supplement.

Evidence grade: Strong. General water needs are an established National Academies reference value, and individualized fluid and mineral limits for people with reduced kidney function are standard guidance from the NIDDK, MedlinePlus and the National Kidney Foundation.

Important: This article is general education. If you have been told your kidney function is reduced, or you are on dialysis, follow the fluid plan your nephrologist or kidney dietitian gives you. Do not change it based on this article.

How Much Water Do Healthy Adults Need?

In 2004 the Institute of Medicine of the National Academies set adequate intakes for total water, meaning water from all beverages and foods. The panel based the values on national data showing that adequately hydrated women consume about 2.7 liters a day and men about 3.7 liters. These amounts cover the expected needs of healthy, sedentary people in temperate climates.

The panel did not set a rule for a certain number of glasses of water. It said most people meet their needs by letting thirst guide them and drinking beverages with meals. Prolonged physical activity and heat raise water losses, and very active people continually exposed to hot weather often need six liters or more a day.

MedlinePlus adds that individual needs depend on sex, weight, age, activity level and any medical conditions you may have.

Fluid Needs at a Glance

Situation	What the sources say	Who sets the amount
Healthy adult women	About 2.7 L (91 oz) total water a day from drinks and food	General reference value; thirst is a reasonable guide
Healthy adult men	About 3.7 L (125 oz) total water a day from drinks and food	General reference value; thirst is a reasonable guide
Very active people in hot weather	Needs can reach 6 L or more a day	Adjust for sweat losses; ask a clinician if you have a medical condition
Earlier stages of reduced kidney function	Fluid often does not need to be limited, but needs vary	Your nephrologist or kidney dietitian
Advanced reduced kidney function or dialysis	Fluid is usually limited because the body cannot remove the extra	Your nephrologist, dialysis nurse or kidney dietitian

How Your Kidneys Regulate Water

Your two kidneys, each about the size of a fist, filter about half a cup of blood every minute. Over a day that adds up to about 150 quarts of blood. Inside each kidney, about a million tiny filtering units called nephrons pass water and small molecules into tubules, which return most of the water and needed substances to the blood. Only 1 to 2 quarts a day leave the body as urine.

The kidneys also keep a healthy balance of water, salts and minerals such as sodium, calcium, phosphorus and potassium in the blood. The NIDDK notes that without this balance, nerves, muscles and other tissues may not work normally.

A hormone helps steer this process. Antidiuretic hormone (ADH) is made in the hypothalamus, stored in the pituitary gland, and acts on the kidneys to regulate how much water is excreted in urine.

Where Your Daily Fluid Comes From

About 80% of total water comes from drinking water and other beverages, including caffeinated ones, and about 20% from food. Water makes up more than two-thirds of the body's weight, helps regulate temperature through sweat, and forms saliva and the fluid around joints.

Many foods count. Soups, melons, grapes, apples, oranges, tomatoes, lettuce and celery all contain a lot of water, and so do foods that are liquid at room temperature or made with a lot of liquid, such as gelatin, pudding and ice cream. MedlinePlus notes that alcohol does not add to the body's water, because it causes the body to release water.

Why Some People Get a Personal Fluid Plan

When the kidneys are damaged, they cannot remove extra fluid as well. The NIDDK explains that people with reduced kidney function may need to limit how much liquid they consume, and that a dietitian or health care professional should work out the right amount for each person.

The amount usually changes over time. MedlinePlus says that in the early stages fluid often does not need to be limited, but as kidney function declines, or once a person is on dialysis, fluid intake needs to be watched. Most people on dialysis urinate very little, so fluid builds up between treatments.

According to the NIDDK, excess fluid between dialysis sessions can cause swelling and weight gain, changes in blood pressure, extra strain on the heart, and fluid in the lungs that makes breathing hard. Dialysis can only remove so much fluid safely at a time, and arriving with too much can cause cramps or a sudden drop in blood pressure.

What research on drinking more water found

Observational studies have linked higher water intake with better kidney function, which led researchers to test it. In the CKD WIT trial, published in JAMA in 2018, 631 adults in Ontario with moderately reduced kidney function were coached either to drink more water or to keep their usual intake. After one year the hydration group's urine volume was about 0.6 liters a day higher, but the decline in kidney function did not differ significantly between groups. The authors noted the study may have been too small to detect a meaningful difference, and several investigators reported funding from Danone Research. The takeaway is that "drink more" is not a universal rule; the right amount is personal.

Sodium, Potassium and Phosphorus Work Together With Fluid

Fluid plans rarely stand alone. The NIDDK and the National Kidney Foundation both describe how kidney care teams also look at sodium, potassium, phosphorus and protein, depending on the stage, blood pressure, lab results and other conditions.

Sodium

Sodium helps control the amount of fluid in the body. Too much makes the body hold on to fluid, which can raise blood pressure and cause swelling. Salt also makes you thirsty, so cutting salty foods such as chips and pretzels makes a fluid limit easier to follow.

Potassium

Reduced kidney function can make it harder to remove potassium, and blood levels can climb too high. Too little or too much potassium can cause heart and muscle problems, so the right amount should be set with a dietitian or clinician. The NIDDK suggests using herbs and spices instead of salt substitutes, which can be high in potassium, and limiting foods with potassium chloride on the label. For background on this mineral, see our article on potassium.

Phosphorus

Damaged kidneys do not clear phosphorus well. High levels can harm blood vessels, weaken bones and cause itchy skin. Phosphorus additives are a major source for many people; the NIDDK suggests checking ingredient lists for "phosphorus" or words containing "PHOS," such as phosphoric acid or disodium phosphate.

Practical Ways to Track Fluid and Manage Thirst

If your care team gives you a daily fluid limit, these tips from the NIDDK and MedlinePlus can help:

Count foods that are liquid at room temperature, such as soup, gelatin and ice cream, plus very watery fruits and vegetables if your team asks you to.
Use smaller cups or glasses, and turn your cup over when you finish it.
Freeze juice in an ice cube tray and eat it like an ice pop, counting the cubes toward your daily fluid.
Avoid salty foods, which drive thirst.
Stay cool on hot days.
Keep a simple log of drinks and fluid-rich foods so you and your team can review it.

Tell your care team if thirst is hard to manage or if you notice swelling in your face, arms, legs or abdomen.

Hydration for Everyday Health and Activity

For people without a fluid limit, hydration mostly comes down to drinking when thirsty, having beverages with meals, and drinking more during heat or long exercise. Our guides to hydration and its role in recovery and hydration strategies for sports performance cover active days in more detail.

Safety and Interactions

Follow the fluid plan your kidney care team gives you. If you have been told your kidney function is reduced, or you are on dialysis, your nephrologist, dialysis nurse or kidney dietitian sets how much fluid, sodium, potassium and phosphorus is right for you. Do not raise or lower your fluid on your own.

Potassium supplements and salt substitutes need clinician approval. The NIH Office of Dietary Supplements warns that in people with impaired potassium excretion from reduced kidney function, even dietary potassium below the adequate intake can cause high blood potassium. Many salt substitutes are high in potassium.
Magnesium supplements need clinician approval. The risk of magnesium toxicity rises when kidney function is impaired, because the body cannot remove the excess.
Over-the-counter supplements on dialysis: The NIDDK advises people on hemodialysis not to take over-the-counter nutritional supplements, because they may contain vitamins or minerals that are harmful. Your provider may prescribe a vitamin made for people with kidney failure instead. Talk with your provider before using probiotics or any supplement.
Medications: Talk to your doctor or pharmacist if you take an ACE inhibitor, an angiotensin receptor blocker or a potassium-sparing diuretic, which can raise potassium. The National Kidney Foundation also notes that some pain relievers, especially NSAIDs, can be harmful to the kidneys; ask before using them.
Warning signs: MedlinePlus notes that too much fluid can lead to shortness of breath, which needs urgent medical care. Report new swelling in your face, arms, legs or abdomen to your care team.

Frequently Asked Questions

How much water should I drink a day?

For healthy adults, the National Academies' adequate intake is about 2.7 liters of total water a day for women and 3.7 liters for men, counting drinks and food. Most people meet this by drinking when thirsty and with meals. If you have a kidney care team, follow the amount they give you.

Does drinking more water help kidney health?

For healthy people, drinking enough to stay hydrated supports normal kidney function. In a 2018 trial of adults with moderately reduced kidney function, coaching them to drink more water did not significantly change kidney function decline after a year. Extra water is not right for everyone, so ask your care team.

Do foods count toward daily fluid?

Yes. About 20% of total water comes from food. Soups, gelatin, ice cream and watery fruits and vegetables such as melons and tomatoes all add to your fluid total.

Why would a kidney care team limit fluids?

When the kidneys cannot remove extra fluid, it builds up and can cause swelling, blood pressure changes, strain on the heart and fluid in the lungs. A personal limit helps keep fluid in balance, especially between dialysis sessions.

Are potassium or magnesium supplements safe if I have kidney concerns?

Not without your clinician's approval. Reduced kidney function makes it harder to clear both minerals, so supplements and potassium-based salt substitutes can push blood levels too high.

How can I manage thirst on a fluid limit?

Cut back on salty foods, use smaller cups, freeze juice into ice cubes that you count toward your total, and stay cool on hot days. Tell your care team if thirst stays hard to manage.

Sources

Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.

Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: October 17, 2026 · How OPA researches and writes