There is no single amount of water that every person should drink before, during and after a workout.

That is not a gap in sports science. It reflects a real biological problem: sweat rate and sweat sodium loss vary substantially between people and can also change with exercise intensity, heat, humidity, clothing and acclimatization. National Athletic Trainers’ Association, 2017 Barnes et al., 2019

The American College of Sports Medicine recommends individualized fluid replacement rather than one universal volume. The main goals are to begin exercise in a normal hydration state, avoid excessive fluid loss during activity, avoid excessive drinking, and replace remaining fluid and electrolyte losses after exercise. ACSM Position Stand

For a short, easy session in a cool environment, drinking according to thirst may be enough for many people. Longer, hotter or more intense exercise can require a more deliberate plan. Kenefick, 2018

Why workout hydration cannot be reduced to one number

A person who walks indoors for 30 minutes and a person who cycles hard for two hours in summer can lose very different amounts of fluid.

Research measuring athletes has documented large differences in whole-body sweat rate across sports and between individuals. In a dataset of 1,303 athletes, average sweat rates differed by sport, with substantial variation inside each group. Barnes et al., 2019

The NATA position statement therefore recommends quantifying individual sweat rate under relevant conditions when a precise plan matters. NATA, 2017

That is the reason rigid rules such as “drink one litre every hour” can be wrong in both directions. For one person that may be too little. For another it may be more than they are losing.

Before exercise: start normally hydrated

The ACSM position stand says the goal before exercise is to begin in a euhydrated state with normal plasma electrolyte levels. When extra pre-exercise fluid is needed, it should be consumed several hours beforehand so the body has time to absorb it and excess urine can be passed before activity begins. ACSM, 2007

This does not mean everyone needs a special pre-workout hydration protocol.

If you have been eating and drinking normally and are not starting a long or demanding session in heat, your usual meals and fluids may already be enough. A pre-exercise plan becomes more useful when previous activity, heat, travel or restricted access to drinks makes it likely that you are starting with a fluid deficit.

A single urine colour check is not a perfect hydration test, but patterns in body mass, thirst, urine frequency and urine concentration can provide context. Sports-medicine reviews recommend combining indicators rather than relying on one sign alone. Maughan and Shirreffs, 2008

During exercise: replace enough, but not too much

During exercise, both underdrinking and overdrinking can cause problems.

The ACSM position stand recommends limiting excessive dehydration, conventionally described as more than about 2% loss of body mass from water deficit, while also avoiding excessive changes in electrolyte balance. ACSM, 2007

NATA similarly advises avoiding both hypohydration and fluid overload. Its position statement says athletes should not finish exercise heavier than they started because weight gain during activity can indicate that fluid intake exceeded fluid loss. NATA, 2017

Short and moderate sessions

A 2018 review comparing planned drinking with drinking to thirst concluded that thirst can be an adequate guide for many shorter or lower-intensity activities, especially those lasting less than about 60 to 90 minutes in cooler conditions. Kenefick, 2018

This should not be interpreted as a hard 90-minute biological threshold. It is a practical distinction from the review, not a rule that applies to every person and environment.

Longer or hotter sessions

Planned drinking becomes more relevant when exercise is longer, more intense, performed in heat, or associated with a high personal sweat rate. The same review recommends that people in those situations estimate sweat losses under conditions similar to the activity they are planning. Kenefick, 2018

The IOC consensus statement on sport in the heat also emphasizes that sweat rate varies widely and makes universal fluid quantities difficult to recommend. IOC Consensus Statement

How to estimate your sweat rate

For repeated training under similar conditions, change in body mass can be used to estimate fluid loss.

The NATA position statement provides a practical method. Weigh yourself before and after exercise, preferably in minimal dry clothing, and account for fluid consumed and any urine produced during the session. NATA, 2017

A simplified estimate is:

sweat loss ≈ body mass lost + fluid consumed - urine produced

If body mass is measured in kilograms and fluid in litres, one kilogram of acute mass change is often treated as approximately one litre for a practical field estimate. For long or very energy-intensive exercise, this approximation becomes less exact because body mass also changes for reasons other than sweat loss. Cheuvront and Montain, 2017

Example:

pre-exercise body mass: 70.0 kg;
post-exercise body mass: 69.5 kg;
fluid consumed: 0.4 L;
no urine during the session.

The field estimate of sweat loss is about 0.9 L over that session.

If the session lasted 90 minutes, the estimated sweat rate is about 0.6 L per hour.

That number is useful only for similar conditions. A hot outdoor run can produce a different sweat rate from an indoor gym session.

Do you need electrolytes during exercise?

Not always.

The 2007 ACSM position stand says beverages containing electrolytes and carbohydrates can provide benefits over water alone in certain circumstances. The need depends on factors such as exercise duration, intensity, sweat losses and the goal of the session. ACSM, 2007

NATA also notes that carbohydrate and electrolyte-containing drinks may be useful during intense or long-duration exercise. NATA, 2017

For an ordinary short workout, plain water is usually a reasonable choice if you are otherwise eating normally. Longer sessions with substantial sweating are a different case.

We cover this distinction in detail in Electrolytes vs Water: When Do You Actually Need Electrolytes?.

Can you drink too much during exercise?

Yes.

Exercise-associated hyponatremia is a potentially dangerous fall in blood sodium associated with exercise. A major risk factor is drinking fluid in excess of losses. The 2015 international consensus statement on exercise-associated hyponatremia specifically addresses prevention of overdrinking. Hew-Butler et al., 2015

This is one reason hydration advice should never be interpreted as “the more the better”.

NATA recommends that physically active people avoid gaining body mass from fluid during exercise. NATA, 2017

After exercise: replace what is still missing

The goal after exercise is to restore any remaining fluid and electrolyte deficit.

How aggressive that replacement needs to be depends on the size of the loss and how soon you need to exercise again. ACSM, 2007

NATA states that when rapid recovery is necessary, especially when the recovery window is shorter than about four hours, replacing roughly 100% to 150% of the calculated fluid loss may be needed because some of the ingested fluid will be lost in urine. When the recovery period is long, normal food and fluids can often restore balance without an aggressive protocol. NATA, 2017

That recommendation is designed for recovery from measurable exercise-related fluid loss. It is not a reason to drink 150% of an arbitrary amount after every workout.

What changes in hot weather?

Heat can increase sweat losses substantially, and the same workout can therefore require a different hydration strategy on a hot day.

The IOC consensus statement recommends that athletes training or competing in heat pay attention to hydration before exercise and recognize that sweat rate depends on temperature, humidity, wind, sun exposure, clothing, metabolic rate and acclimatization. IOC, 2023

Our separate guide, How Much Water Should You Drink in Hot Weather?, covers heat outside the exercise setting as well.

What does a sensible plan look like for ordinary exercise?

For a healthy adult doing recreational exercise, the evidence supports a flexible approach rather than a fixed bottle quota.

Before exercise: arrive normally hydrated. If you know you are starting low on fluid, correct that several hours before the session rather than immediately beforehand.

During a short or easy session: drink when thirsty and make water available.

During longer, harder or hotter exercise: consider a planned strategy based on your own sweat rate and the conditions.

After exercise: replace remaining losses, using normal food and fluids when recovery time is generous and a more deliberate strategy when losses are large or another session is soon.

At every stage: avoid drinking enough to gain weight during exercise.

When general advice is not enough

Individual medical guidance matters if you have kidney disease, heart disease, a condition that affects sodium or fluid balance, or take medicines that alter urination or electrolytes.

Competitive endurance events, very high heat, repeated sessions, and unusually high sweat losses can also justify individualized sports-nutrition or medical advice.

A general hydration article cannot safely convert those situations into one universal formula.

Sources and further reading

This article is general information for healthy adults. People with medical conditions affecting fluid or electrolyte balance should follow individual advice from their healthcare professional.