Hydration supports recovery by replacing the water and sodium you lose in sweat, so blood volume and temperature control can return to normal. Most healthy adults stay hydrated day to day by drinking to thirst and with meals.[1] After hard or hot exercise, the best-supported approach is to drink somewhat more than you lost, together with some sodium.[6][7]
Key Takeaways
- The National Academies set an Adequate Intake for total water, from drinks and food, of about 3.7 liters a day for men and 2.7 liters for women.[1]
- During exercise, the American College of Sports Medicine (ACSM) advises avoiding a water loss of more than 2% of body weight. Weighing yourself before and after a session shows roughly how much you sweat.[6]
- After exercise, drinking more than you lost restores fluid balance only when the drink or meal also supplies enough sodium.[7]
- Coffee, tea and milk count toward your fluid intake. In one trial, moderate coffee hydrated habitual coffee drinkers about as well as water.[8][9]
- Urine color is a reasonable everyday check, but it is not a precise test.[11]
- Drinking far more than you sweat out can dilute blood sodium, which can be dangerous.[1][12]
Evidence grade: Strong. Daily fluid needs rest on National Academies reference values, and exercise rehydration advice comes from an ACSM position stand and controlled rehydration trials in people.
How Much Fluid Do You Need Each Day?
The Institute of Medicine (now the National Academies) did not find enough evidence to set an exact requirement for water. Instead, it set an Adequate Intake (AI) based on what healthy Americans actually consume. For adults aged 19 to 30, the AI for total water is 3.7 liters a day for men and 2.7 liters for women. That total includes water in food. Beverages and plain water supplied about 3.0 liters (roughly 13 cups) for men and 2.2 liters (about 74 fluid ounces) for women.[1]
About 80% of total water comes from drinks, and the rest comes from food. Day to day, thirst and drinking with meals keep most people's body water at normal levels. People who are physically active or spend time in the heat need more.[1]
What Happens to Fluid and Sodium When You Exercise
Sweat cools you, but it also takes water and electrolytes with it, mainly sodium. Sweat rates and sweat electrolyte content vary a lot from person to person, so the ACSM recommends customized plans rather than one fixed amount.[6] Potassium is different: only a very small amount is lost in sweat.[3]
The ACSM's goal for drinking during exercise is to prevent a water loss of more than 2% of body weight, which can hurt performance. You can estimate your own sweat rate by weighing yourself before and after a typical session.[6] For longer events, see our guide to electrolyte management during long-distance races, and for team and gym sports, our article on hydration strategies for sports performance.
Rehydrating After Exercise
After exercise, the aim is to replace whatever fluid and electrolyte deficit is left. How fast you need to do it depends on how big the deficit is and how soon you train or compete again.[6] If your next session is the next day, normal meals and drinks usually give your body time to catch up. If it is in a few hours, a more deliberate plan helps.
A classic rehydration trial shows why volume alone is not enough. Twelve men lost about 2% of their body mass through cycling. They then drank 50%, 100%, 150% or 200% of that loss as a lower-sodium (23 mmol/L) or higher-sodium (61 mmol/L) drink. Restoring fluid balance took more fluid than was lost in sweat. Unless the drink had enough sodium, much of the extra simply came out as urine.[7]
Drinks also differ in how much of the fluid your body keeps. In a randomized trial of 72 men, an oral rehydration solution and full-fat or skim milk led to less urine over four hours than the same volume of still water. Coffee, tea, cola, orange juice, sparkling water and a sports drink were no different from water.[8]
| Option | What it supplies | What the research shows |
|---|---|---|
| Water | Fluid only | The comparison standard; pair it with a meal or snack for sodium[7][8] |
| Milk (full-fat or skim) | Fluid, protein, carbohydrate, electrolytes | More of it stayed in the body over 4 hours than the same volume of water[8] |
| Oral rehydration solution | Fluid, sodium, some sugar | Retained better than water over 4 hours[8] |
| Sports drink | Fluid, carbohydrate, some sodium | Same as water in people who were already hydrated; can help over water during exercise in some situations[6][8] |
| Coffee or tea | Fluid, caffeine | Counts toward fluid intake in moderate amounts[1][8][9] |
| Electrolyte powder in water | Fluid plus the electrolytes on the label | Adds sodium, which helps the body hold on to rehydration fluid[7] |
Why Sodium Matters for Recovery
Sodium is what helps your body keep the fluid you drink after exercise.[7] For everyday health, the National Academies set the sodium AI for adults at 1,500 mg a day. They advise cutting back if you regularly eat more than 2,300 mg a day.[2] People who are not used to heat and who exercise for long periods in hot weather may need more, because they lose more in sweat.[1]
A salted meal with water works for most people. Some prefer an electrolyte drink mix. OPA's ION+ Select Electrolyte Powder is one option. It is a scoop-and-mix powder with magnesium (as di-magnesium malate), potassium (as potassium chloride), sodium from Himalayan pink salt and vitamin B12, plus coconut water, beet root and acerola juice powders. It has no added sugars or stimulants and is designed to support hydration after workouts, during fasting windows and on active days. For more on potassium in food, see our guide to potassium benefits.
Hydration Myths Checked Against the Evidence
Myth: Everyone needs eight glasses of plain water a day
A review that went looking for the origin of the "8 x 8" rule found no scientific studies supporting it for healthy adults in a temperate climate who are not very active. Caffeinated drinks can count toward the total. The same review notes that hard work, exercise and hot climates do call for more fluid.[10] The National Academies' AI covers all drinks and food, not plain water alone.[1]
Myth: Coffee dehydrates you
The National Academies concluded that any diuretic effect of caffeinated drinks may be short-lived, and that these drinks still add to total water intake.[1] In a crossover trial, 50 men who usually drank 3 to 6 cups a day had four 200 mL cups of coffee daily for three days, then water. Total body water, 24-hour urine volume and other hydration markers did not differ between the two.[9] The trial included only men who were used to caffeine, and it tested moderate amounts.
Myth: If you feel thirsty, you are already dehydrated
Thirst is a finely tuned signal that responds before your blood becomes more than a few percent more concentrated. The 2015 international consensus on exercise and low blood sodium recommends drinking to thirst for most athletes, and notes that mild fluid losses of up to 2% to 3% of body weight are generally well tolerated.[12] In long or very hot sessions, a planned drinking schedule based on your measured sweat rate is a reasonable alternative.[6]
Myth: Your urine color tells you exactly how hydrated you are
Urine color does track the lab measures of urine concentration. Researchers judged it good enough for sports and field use, but not precise enough for the lab.[11] Darker yellow urine, together with thirst and a dry mouth, is a common sign of mild to moderate fluid loss.[4]
Myth: You cannot drink too much water
You can. The healthy kidney can excrete only about 0.7 to 1.0 liter of water an hour. Drinking much faster than that, or overdrinking during very long exercise, can dilute blood sodium to dangerous levels.[1] The safety section below covers this.
Hydration When Recovering From Illness or Surgery
Fever, vomiting and diarrhea all raise fluid losses. Being unwell can also make you less likely to eat or drink, and older adults are at higher risk of running low.[4] After a procedure, your surgical or medical team's fluid instructions come first, because needs at that time are individual. Food matters during recovery too; see our articles on protein intake for wound healing and vitamins and minerals for post-surgical recovery.
A Simple Recovery Hydration Routine
- Start sessions well hydrated. If you need to drink extra beforehand, do it several hours ahead so your body can absorb it and pass any excess.[6]
- Weigh yourself before and after a few typical workouts to learn your sweat rate.[6]
- During exercise, drink to thirst, or to a plan that keeps losses under about 2% of body weight without gaining weight.[6][12]
- Afterward, replace the deficit with fluid plus sodium from food or an electrolyte drink, especially when the next session is only hours away.[6][7]
- Count milk, coffee, tea and water-rich foods toward your total.[1][8]
Safety and Interactions
Overdrinking. Low blood sodium makes cells swell, and brain cells are especially sensitive. Symptoms include confusion, headache, nausea, vomiting, fatigue, muscle weakness or cramps and, in severe cases, seizures.[5] Exercise-related cases are typically linked to more than six hours of hard, prolonged exercise.[1] They are uncommon, but they can be fatal, and excessive fluid intake is the main driver.[12] Anyone who becomes confused or vomits after drinking large amounts needs prompt medical care.
Severe fluid loss. Not urinating, very dark urine, dizziness, a rapid heartbeat or confusion can signal severe dehydration, which is a medical emergency.[4]
Medications and medical conditions. Talk to your doctor or pharmacist before changing your fluid or electrolyte intake if you take diuretics (water pills), which increase urine and sodium losses.[4][5] Electrolyte products that contain potassium need the same conversation if you take ACE inhibitors, angiotensin receptor blockers or potassium-sparing diuretics such as spironolactone or amiloride, because these medicines can raise blood potassium.[3] The potassium AIs do not apply to people whose kidneys do not clear potassium normally.[3] If your doctor has given you a fluid or sodium limit, follow that limit over any general guidance here.
Frequently Asked Questions
How much water should I drink a day?
The National Academies' Adequate Intake for total water is about 3.7 liters a day for men and 2.7 liters for women. That includes all drinks and the water in food, and about 80% of it usually comes from drinks. Most healthy people meet their needs by drinking to thirst and with meals. You need more when you are active or in the heat.
How much should I drink after a workout?
Weigh yourself before and after. Research shows you need to drink somewhat more than the weight you lost to fully rehydrate. That extra fluid stays in your body better when it comes with sodium from food or an electrolyte drink. If your next session is a day away, normal meals and drinks usually cover it.
Does coffee count toward hydration?
Yes, in moderate amounts. The National Academies count caffeinated drinks toward total water intake. A crossover trial in habitual coffee drinkers found four cups a day hydrated about as well as water. Very large caffeine doses were not tested.
Is thirst a reliable guide to drinking?
For most people and most workouts, yes. Thirst responds early to small changes in blood concentration, and the 2015 international consensus panel on exercise and low blood sodium recommends drinking to thirst. For very long or very hot sessions, a plan based on your measured sweat rate is a reasonable alternative.
Do I need an electrolyte drink to recover?
Not always. A meal that contains salt, eaten with water, supplies the sodium your body needs to keep rehydration fluid. Electrolyte drinks are a convenient option after heavy sweating or when you need to rehydrate quickly before another session.
Can you drink too much water?
Yes. The kidneys can excrete only about 0.7 to 1.0 liter an hour. Drinking much more than you lose, especially during long endurance events, can dilute blood sodium to dangerous levels. Drink to thirst, and avoid drinking so much that you gain weight during exercise.
Sources
- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (Summary). National Academies Press. 2005.
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium (Summary). National Academies Press. 2019.
- NIH Office of Dietary Supplements. Potassium: Fact Sheet for Health Professionals.
- MedlinePlus Medical Encyclopedia. Dehydration. National Library of Medicine.
- MedlinePlus Medical Encyclopedia. Low blood sodium. National Library of Medicine.
- American College of Sports Medicine; Sawka MN, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007.
- Shirreffs SM, Taylor AJ, Leiper JB, Maughan RJ. Post-exercise rehydration in man: effects of volume consumed and drink sodium content. Med Sci Sports Exerc. 1996.
- Maughan RJ, et al. A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. Am J Clin Nutr. 2016.
- Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One. 2014.
- Valtin H. "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 x 8"? Am J Physiol Regul Integr Comp Physiol. 2002.
- Armstrong LE, et al. Urinary indices of hydration status. Int J Sport Nutr. 1994.
- Rosner MH. Preventing deaths due to exercise-associated hyponatremia: the 2015 consensus guidelines. Clin J Sport Med. 2015.
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: · How OPA researches and writes
