Hydration is often discussed in very simple terms—“drink more water”—yet the relationship between fluid balance and performance is more nuanced than that. Even mild dehydration can increase perceived effort and impair endurance, strength, and decision-making, while excessive fluid intake can, in rare cases, lead to dangerous electrolyte disturbances such as exercise-associated hyponatremia.
For athletes and physically active people, the goal is not to drink as much as possible, but to maintain an appropriate balance: enough fluid and electrolytes to support performance and thermoregulation, without drifting into chronic dehydration or overhydration. Position stands from organizations such as the American College of Sports Medicine (ACSM) and public health guidance from national bodies now emphasize individualized strategies over rigid, one-size-fits-all rules.
Below are 10 best practices for hydration and performance, based on current evidence and practical considerations. They are intended for healthy adults; anyone with medical conditions (especially kidney, heart or endocrine disorders) should follow individualized medical advice.
1. Know your daily baseline needs
Before thinking about training, it is helpful to understand your general daily fluid requirements. The U.S. National Academies of Sciences, Engineering, and Medicine suggests that, under temperate conditions, total fluid intake (from beverages and food) of about 3.7 liters per day for men and 2.7 liters per day for women is adequate for most healthy adults. Roughly 20% of this typically comes from food, especially fruits and vegetables.
These values are general estimates, not strict targets. Fluid needs increase with higher activity levels, hot or humid environments, and illness (such as fever, vomiting or diarrhea). They may be somewhat lower in smaller or less active individuals.
As a starting point:
- Use the guideline ranges as broad reference values.
- Recognize that “adequate intake” is a range, not a precise figure.
- Remember that water, other beverages and high-water foods all contribute to your total.
From this baseline, you then adjust for training demands.
2. Start exercise in a well-hydrated state
ACSM guidance emphasizes beginning exercise euhydrated—that is, with normal body water and electrolyte levels. This reduces cardiovascular strain, helps maintain core temperature, and supports both endurance and strength performance.
Practical strategies include:
- Drink fluids regularly throughout the day rather than consuming a large volume immediately before training.
- In the 2–4 hours before exercise, consume approximately 5–10 mL of fluid per kilogram of body mass (for a 70-kg person, 350–700 mL), adjusting for thirst, environment and prior intake.
- Check that urine is pale straw-colored rather than very dark; this is a simple, imperfect but helpful indicator that you are not starting in a markedly dehydrated state.
Very large fluid boluses immediately before strenuous exercise can be uncomfortable and may increase the need for bathroom breaks. A gradual approach is generally better.
3. Use thirst and simple monitoring, not rigid rules
For many years, athletes were encouraged to “stay ahead of thirst” and drink according to fixed schedules. More recent reviews and expert statements highlight that thirst is a useful cue for most individuals and that rigid over-drinking can increase the risk of hyponatremia, particularly in long events.
ACSM and other experts now suggest combining internal and external indicators:
- Thirst: a primary signal that fluid intake should increase.
- Body weight changes around exercise:
- A loss of more than ~2% of body mass during a session indicates that dehydration is likely sufficient to impair performance for many people.
- A weight gain during prolonged events suggests overhydration, which can be associated with hyponatremia.
- Urine color and frequency over the day, as a simple, approximate gauge of hydration status.
Rather than aiming to drink a fixed amount each hour regardless of conditions, a more flexible approach is to:
- Begin exercise hydrated.
- Drink according to thirst and planned access to fluids.
- Adjust volume to keep body mass changes within a reasonable range (often within 0–2% loss for most training sessions).
4. Match fluid intake to sweat loss during exercise
Sweat rates vary widely among individuals—from less than 0.5 liters per hour to more than 2 liters per hour in hot conditions. Because of this variability, “one bottle per hour” formulas are often inaccurate.
A simple way to estimate your sweat rate is:
- Weigh yourself (ideally with minimal clothing) before exercise.
- Perform your usual training session, tracking any fluid consumed.
- Weigh yourself again afterward, in similar clothing and conditions.
Each 1 kg of body mass lost corresponds to approximately 1 liter of fluid deficit, not counting fluids consumed. From this, you can estimate how much fluid you typically lose per hour in those conditions and aim to replace enough to limit body mass loss to around 2% or less in most situations.
For many training sessions of up to about an hour in cool to moderate environments, drinking according to thirst is sufficient. For longer or more intense sessions, particularly in heat, having an approximate idea of your sweat rate helps to refine your hydration plan.
5. Do not overlook the risk of overhydration
Dehydration is a well-known problem; overhydration is less discussed but increasingly recognized. Exercise-associated hyponatremia (EAH) occurs when blood sodium concentration becomes abnormally low, often due to excessive intake of low-sodium fluids relative to sweat losses, combined with impaired water excretion.
EAH has been reported most frequently in slower participants in endurance events, who sometimes drink continuously “just in case,” surpassing their actual sweat losses. Symptoms range from mild (nausea, headache, confusion) to severe (seizures, coma), making prevention important.
To reduce the risk:
- Avoid drinking so much during exercise that your body weight increases relative to pre-event measurements.
- Use thirst as a guide rather than drinking to a fixed, high target.
- In long events, include electrolytes—particularly sodium—in your fluid or food strategy (see next section).
The goal is balance: enough fluid to avoid substantial dehydration, but not so much that dilutional hyponatremia becomes a risk.
6. Use electrolytes strategically, especially for long or hot sessions
Sweat contains not only water but also electrolytes, particularly sodium. During long or intense exercise, especially in hot and humid environments, sodium losses can be considerable.
Reviews of electrolyte needs suggest that including sodium in fluids or foods during prolonged exercise can help maintain plasma volume, support thermoregulation, and reduce the risk of hyponatremia. However, the exact amount required varies by individual sweat rate and sweat sodium concentration.
Practical guidance includes:
- For training sessions longer than about 60–90 minutes, especially in heat, consider using:
- A sports drink containing sodium (and carbohydrate), or
- Water plus salty snacks or other sodium-containing foods.
- In shorter, moderate-intensity sessions under temperate conditions, water alone is usually sufficient.
- Be cautious with very high sodium intakes if you have hypertension or other cardiovascular risk factors; follow medical advice in these cases.
Electrolyte products are widely available, but more is not always better. The objective is to replace a portion of what is lost, not to load sodium beyond normal needs.
7. Choose the right type of beverage for the situation
Not all fluids behave the same way in the body. Beverages vary in osmolality (concentration of particles), carbohydrate content, and electrolyte composition, all of which influence how quickly they are absorbed and how suitable they are for different purposes.
Broadly:
- Plain water
- Appropriate for most daily hydration and for shorter or lower-intensity sessions.
- Does not provide carbohydrate or electrolytes, which may be needed in prolonged exercise.
- Hypotonic or isotonic sports drinks
- Contain moderate carbohydrate (often around 4–8%) and electrolytes.
- Designed to replace both fluid and some energy and sodium during longer or more intense sessions, with good absorption characteristics.
- Hypertonic drinks or very sugary beverages
- High carbohydrate concentration can slow gastric emptying and may cause gastrointestinal discomfort if consumed in large quantities during exercise.
- Often better suited to post-exercise energy replacement than to mid-session hydration.
Evidence suggests that isotonic and slightly hypotonic drinks can be effective for rehydration and performance in endurance settings, while plain water is generally sufficient in shorter or less demanding contexts.
Alcoholic and very high-sugar beverages are not recommended around training, as they can impair hydration status, sleep and recovery.
8. Plan hydration before, during, and after exercise
Hydration for performance is not limited to what happens during a training session. It is helpful to think in terms of three phases: before, during, and after.
Before exercise
- Aim to start euhydrated using the strategies described earlier.
- Avoid very large, rapid fluid intakes immediately before intense exercise.
During exercise
- For sessions shorter than about an hour:
- Drink according to thirst and access, which may require little or no fluid in cool, low-intensity situations.
- For longer or hotter sessions:
- Use your estimated sweat rate and body mass changes to guide intake, aiming to limit losses to around 2% of body mass.
- Include electrolytes and, where appropriate, carbohydrates.
After exercise
- The aim is to replace the remaining fluid deficit. ACSM guidance suggests consuming roughly 1.25–1.5 liters of fluid per kilogram of body mass lost over the hours following exercise to fully restore body water.
- Including sodium in post-exercise meals or drinks helps retain the ingested fluid and restore electrolyte balance.
You do not need to calculate these values after every minor session, but they are useful reference points after particularly long, hot or demanding training or competition.
9. Adjust for environment, intensity and individual factors
Hydration strategies should be context-dependent. Several factors influence fluid needs:
- Environmental conditions:
- Heat and humidity increase sweat rates and electrolyte losses.
- Cold environments can sometimes blunt thirst, even when fluid losses remain substantial.
- Exercise type and intensity:
- High-intensity and endurance activities generally produce higher sweat rates than light, intermittent efforts.
- Individual characteristics:
- Body size, fitness level, acclimatization to heat, and even genetic factors affect sweat rate and composition.
Public health guidance (for example, from the CDC and Harvard) emphasizes that fluid needs cannot be reduced to a single number and must be tailored to activity, climate, health status and life stage.
A practical approach is to treat general recommendations as a baseline, then adjust systematically:
- Observe your response in different conditions (performance, perceived exertion, body weight changes).
- Modify fluid and electrolyte intake as you gain more information about how your body behaves.
- Reassess during seasonal changes (for example, winter to summer training).
10. Build consistent habits and let performance guide fine-tuning
Ultimately, hydration for performance is not only about science but also about habit. The best plan is one that you can implement consistently.
Helpful strategies include:
- Keeping water readily available during the day, not only at training times.
- Integrating hydration with meals and snacks rather than relying solely on drinking between them.
- Using simple cues—urine color, thirst, and small weight changes—to prompt adjustments, rather than trying to memorize complex formulas.
- Observing how changes in your hydration routine affect performance, recovery and comfort over several sessions, not just one.
Systematic reviews indicate that both hypohydration and overhydration can impair not only physical output but also cognitive functions such as vigilance, decision-making and mood. These effects are particularly relevant in sports and occupations where rapid judgment and sustained concentration are important.
As you refine your own strategy, it can be useful to:
- Keep brief notes on training sessions that feel unusually strong or unusually difficult, including environmental conditions and how you handled hydration.
- Make incremental changes rather than large, abrupt shifts.
- Revisit evidence-based guidelines periodically to ensure that your habits remain aligned with current understanding.
Final considerations
Hydration is not a separate concern from training; it is a part of it. The research now paints a clear picture: maintaining an appropriate fluid and electrolyte balance supports cardiovascular function, thermoregulation, muscular performance and cognitive clarity, while both significant deficits and excesses can impair these systems.
The best practices outlined here—understanding baseline needs, starting exercise well hydrated, using thirst and monitoring tools, matching intake to sweat loss, avoiding overhydration, using electrolytes appropriately, choosing suitable beverages, planning hydration around training, adjusting for context, and building consistent habits—offer a framework rather than a rigid prescription.
Within that framework, there is room for individual variation. Over time, a thoughtful approach to hydration becomes less about rules and more about knowing your own responses. That knowledge, combined with the evidence available, allows hydration to support performance reliably, rather than being a source of uncertainty or risk.
