Water is a good start, but it’s not always enough on its own. When you sweat heavily, you lose both fluid and electrolytes, especially sodium. The best drink depends on how much you sweated and for how long, but in most cases, a beverage with some sodium will rehydrate you faster and more completely than plain water.
What You Actually Lose in Sweat
Sweat is mostly water, but it carries a meaningful amount of minerals with it. Sodium is the big one. Whole-body sweat sodium concentration ranges from roughly 230 to 1,600 mg per liter, with most people falling somewhere in the middle. You also lose smaller amounts of potassium and chloride. The exact concentration varies widely from person to person and depends on fitness level, heat acclimatization, genetics, and how hard you’re working.
This matters because sodium helps your body hold onto the fluid you drink. Without it, a large portion of what you consume passes straight through to your bladder. In one study comparing skim milk (which naturally contains sodium and potassium) to plain water during exercise in the heat, participants who drank water produced nearly three times more urine (220 mL vs. 81 mL) and ended up more dehydrated despite drinking similar volumes.
When Plain Water Is Fine
If you sweated for less than an hour at a moderate intensity, plain water paired with your next meal will typically cover your losses. Food contains sodium and other minerals, so a normal meal handles the electrolyte side of the equation. The key is not to overthink short, everyday bouts of sweating. A walk on a hot day, a 30-minute gym session, yard work: water is enough.
When You Need More Than Water
Electrolyte replacement becomes more important after prolonged or intense sweating, roughly 60 minutes or more of continuous activity, especially in heat. The same goes for situations where you won’t be eating a meal soon after. In these cases, a drink containing sodium helps your intestines absorb fluid faster and signals your kidneys to retain more of it.
Sports drinks with electrolytes score about 15% higher than plain water on the Beverage Hydration Index, a measure of how well a drink keeps you hydrated over several hours. That edge comes almost entirely from the sodium and the small amount of sugar, which work together to pull water across the intestinal wall more efficiently.
For rapid rehydration when you’re significantly dehydrated, sports medicine guidelines recommend a sodium concentration between 20 and 30 milliequivalents per liter in your recovery drink. If you’re moderately dehydrated with limited time before your next session, a slightly saltier drink (40 to 60 milliequivalents per liter) improves fluid retention even further. Most commercial sports drinks fall in the lower range, which works well for the average person.
Your Best Options, Ranked
- Sports drinks or electrolyte mixes: The most straightforward option. They provide sodium, potassium, and a small amount of carbohydrate in concentrations designed for absorption. Look for one with at least 400 to 500 mg of sodium per liter.
- Milk: Skim or low-fat milk is surprisingly effective. Its natural sodium and potassium fall within the ranges recommended for sports drinks (10 to 35 mmol/L sodium, 3 to 5 mmol/L potassium), and its protein and slight calorie content slow gastric emptying, keeping fluid in your system longer. Multiple studies show it outperforms water for fluid retention.
- Coconut water: High in potassium (about 1,420 mg per liter, roughly ten times what a sports drink contains) but relatively low in sodium (448 mg/L, comparable to a sports drink). This makes it a decent option for general rehydration but less ideal when your primary loss is sodium from heavy sweating. If you prefer coconut water, adding a pinch of salt closes the gap.
- Water with salty food: A glass of water alongside pretzels, salted nuts, soup, or a regular meal works well. The food supplies the sodium your body needs to retain the fluid. This is the most practical approach for many people.
- Plain water: Always appropriate for mild to moderate sweating. Just be aware that drinking large volumes of plain water without any sodium source after extended heavy sweating can, in rare cases, dilute your blood sodium to dangerous levels.
How Much to Drink
A useful rule of thumb: drink 16 to 24 ounces of fluid for every pound of body weight you lost during activity. If you don’t have a scale handy, your urine color is a reasonable guide. Pale yellow means you’re well hydrated. Dark yellow or amber means you need more fluid.
For rapid rehydration, especially if you have another workout or event coming up within a few hours, aim to drink about 150% of the fluid you lost. You need more than a one-to-one replacement because your body continues producing urine even as you rehydrate. Spread this intake over the first two to three hours rather than chugging it all at once.
The Risk of Drinking Too Much Plain Water
Exercise-associated hyponatremia occurs when blood sodium drops below 135 mmol/L, typically because someone drank far more plain water than they lost in sweat. It’s most common during endurance events like marathons and long hikes, and symptoms range from nausea and headache to confusion and, in severe cases, seizures. The safest strategy is to drink based on thirst rather than forcing fluids on a fixed schedule. Pairing water with salty foods or choosing a sodium-containing beverage reduces the risk significantly.
Timing and Temperature
Start rehydrating within the first 15 to 60 minutes after exercise, then continue sipping over the next two to three hours. You don’t need to replace everything immediately. Eating water-rich fruits and vegetables (watermelon, oranges, cucumbers) during this window contributes to your total fluid intake as well.
Beverage temperature is largely a matter of preference. Research on gastric emptying shows that cold drinks (around 40°F) leave the stomach slightly more slowly than room-temperature or warm beverages in the first 5 to 10 minutes, but the difference is small and evens out quickly. Drink whatever temperature you’ll actually consume more of, since volume matters more than temperature for rehydration.