How Much Water Should Runners Drink? Before, During and After a Run

Most runs under an hour need no water on the way. Start the run hydrated, drink when you get home, and you are done; longer runs, hot days and races up to a half marathon need a plan built on your own sweat.

This page covers training runs and races up to 21.1 km (13.1 miles). For the rules behind any workout, from the gym to a bike ride, see how much water to drink before, during and after a workout.

How Much Water Should You Drink Before a Run?

No extra amount. The National Athletic Trainers' Association (NATA) says recreational athletes "should not need to consume extra fluids before activity" but should start hydrated. Your normal drinks the day before and your usual morning glass do that job, and pale yellow pee tells you it worked.

The CDC puts the check simply: light yellow or clear pee "usually means you are drinking enough water".

If you do want extra before a long run, the American College of Sports Medicine (ACSM) says to start "at least several hours before the activity". That gives your body time to absorb it and your pee time to return to normal. A big bottle at the start line leaves no time for either.

How Much Water Should You Drink During a Run?

Enough to keep your weight loss under 2 %, and never more than you sweat. NATA says about 200 ml (7 oz) every 15 to 20 minutes "may be ideal" on longer sessions. For a 70 kg (154 lb) runner, 2 % is 1.4 kg, which means about 1.4 L of sweat left unreplaced.

Why 2 %? In the studies of long aerobic exercise that NATA reviewed, performance dropped consistently once people lost 2 % of their body mass or more. The upper limit matters as much: NATA tells active people not to drink more than the weight they lose.

How Much Runners Sweat

The range is wide, from the US National Academies figures for distance runners to NATA's range for all adults:

0.7 L

women distance runners, mild weather

1.0 L

men distance runners, mild weather

1.0–2.0+ L

male competitive runners in the heat

0.5–4.0 L

adult range in exercise

Two runners on the same route can need very different amounts, which is why a fixed number of sips fails half the field.

Your own number takes one scale and one run: weigh yourself before and after an hour of running, and how to calculate your sweat rate turns the difference into litres per hour.

Thirst or a Plan?

On an easy run, thirst is enough. In a race, it lags: NATA warns that "drink when thirsty" may cost competitive athletes some performance, because thirst can come late.

When people drink only as they want during exercise, NATA notes, they replace roughly two-thirds of what they sweat. On a 30-minute jog that gap is tiny. Across a two-hour half marathon it adds up, so race day is when a plan beats instinct.

Whether thirst works for the rest of your day is a separate question, answered in is thirst a good guide.

Should You Drink Water During a 5K?

Usually not. NATA says activity lasting less than an hour should need "no substances other than water", and at an easy 6 minutes per kilometre a 5K takes 30 minutes; at 1.0 L of sweat an hour, that run costs about 0.5 L, under 1 % of a 70 kg runner's weight. Take a sip at the water station if it is hot or you feel thirsty.

Here is the same runner, Sam (70 kg, about 1.0 L of sweat an hour), across the distances people train for.

The line sits somewhere past the hour. Below it, you carry water for comfort; above it, you carry it because the 2 % mark comes into reach.

How Much Water Should You Drink for a Half Marathon?

Drink enough to finish less than 2 % lighter than you started, and never heavier. NATA's pace of about 200 ml (7 oz) every 15 to 20 minutes is the starting point, and your sweat rate decides whether you need all of it. A smaller runner who sweats less often needs fewer sips than the NATA pace.

Sam, a 2-Hour Half on a Mild Morning

Sam loses about 2.0 L over the race. His 2 % mark is 1.4 kg, so he has to drink at least 0.6 L, and no more than the 2.0 L he sweats.

He takes 200 ml at every 20-minute mark, six drinks in all. That adds up to 1.2 L, and he crosses the line 0.8 kg (1.1 %) lighter: inside both limits.

Ana, a 2.5-Hour Half

Ana weighs 55 kg (121 lb) and sweats about 0.7 L an hour, so she loses about 1.75 L. Her 2 % mark is 1.1 kg: she needs at least 0.65 L.

If she copied a "200 ml every 15 minutes" rule, she would drink 2.0 L, more than she sweats, and finish heavier. NATA warns against exactly that. At 150 ml (5 oz) every 20 minutes she drinks about 1.1 L and finishes about 1.2 % lighter.

Water or Sports Drink on Race Day?

NATA says sessions longer than an hour, or with hard intervals, may benefit from added carbohydrate or electrolytes. Whether that applies to your half, and how much salt sweat really costs, is covered in when you need electrolytes.

Running in Heat and in Cold

Change the plan when the weather turns:

• Heat: the CDC's advice for athletes is to run earlier or later in the day and to "drink more water than usual". The National Academies' figures for male runners rise from about 1.0 L an hour in mild weather to 1.0 to more than 2.0 L in the heat; drinking in hot weather has the rest.
• Cold: NATA notes that thirst is blunted in cold weather, so you drink less than you need without noticing. The reasons and the fixes are in dehydration in cold weather.

What to Drink After a Run

Replace what the scale says you lost, plus a margin. NATA advises drinking 100 % to 150 % of the weight lost, toward 150 % when your next session is less than 4 hours away. With more than 12 hours to recover, normal meals and drinks bring you back.

Sam finished his half 0.8 kg lighter, so he drinks 0.8 to 1.2 L (27 to 41 oz) over the next few hours, not all at once. For the pace and the best drinks, see how to rehydrate.

When Drinking More Becomes the Problem

Drinking far more than you sweat dilutes the sodium in your blood. NATA calls this exercise-associated hyponatremia and says it comes from "excessive consumption of hypotonic fluids (including sports drinks)". It shows up in 10 % to 20 % of sampled marathon finishers, though serious cases are uncommon.

NATA reports it more often in women and after activity longer than 4 hours. Most half marathons finish well inside that window, and the weigh-in rule (never finish heavier) protects you either way.

Your Everyday Goal on Running Days

Race-day sips sit on top of your normal day. Glubbo's habit formula sets that everyday goal from your weight, activity, climate and sex; on the High activity setting it adds 300 ml to the base.

• Sam, 70 kg, High activity, mild climate, male: 2,550 ml (86 oz) a day.
• Ana, 55 kg, High activity, mild climate, female: 1,800 ml (61 oz) a day.

The formula is a habit target, not a sweat test, so a long run still calls for its own plan. Where the official daily numbers come from is in how much water you should drink a day. The water intake calculator gives your own goal, and bottles per day turns it into refills of the bottle you run with.

What to Do This Week

1. Weigh yourself, without shoes, before your next one-hour run.
2. Note what you drink on the way, then weigh yourself again.
3. Add the drinks to the weight lost: that is your sweat for one hour.
4. Use it to set your sips for your longest run, and practise the plan there before race day.