How Much Water Should You Drink With an Energy Gel?

A 25-Gram Gel Needs About 300 mL of Water

Research has shown that the best carbohydrate concentration is 6 to 8 percent, which is 6 to 8 grams of carbohydrate in every 100 mL of water. That's why the custom fueling plans CarbRate creates for you make sure every gel you take is at the optimal concentration.

To achieve an 8% concentration, that means you'll need 100 mL (3.5 oz) of water for every 8 grams of carbohydrate. A typical gel has 25 grams in it, so you want about 300 mL (10 oz) of water with each one.

Gels aren't all 25 grams. They can contain anywhere from 22 to 40 grams of carbs, so check the label on the one you plan to use and adjust your water intake based on how many carbs it has. You can compare the grams in every gel with our free fuel finder.

Work it out once, before race day, so you aren't doing the arithmetic on the course:

• Read the carbohydrate per gel on the label.
• Divide it by 8, then multiply by 100 mL. That is your water per gel.
• Divide that by 100 mL (3.5 oz), about what one aid-station cup gives you, to count the cups you need at each table.

If your hourly target is not set yet, our free fueling plan works it out from your body and goal time, and tells you how many gels that makes.

Why a Gel Needs the Water

A gel is concentrated carbohydrate, and it needs fluid to leave your stomach. The water you take with it brings the mix down to the 6 to 8 percent range.

Researchers have tested where the top of that range is. In a 1999 study, 14 people rode a bike for 90 minutes and drank water or a 4%, 6% or 8% carbohydrate drink every 15 minutes.3

The 8% drink left their stomachs more slowly than the 4% and 6% drinks. The researchers also found that how much carbohydrate a drink carried mattered more for this than whether it was isotonic.

That means 8% is the strongest mix you want in your stomach, and a gel washed down with a few sips of water is far stronger than that.

The reason having an optimal concentration is so critical is that blood flow to your gut drops about 20% in the first 10 minutes of running and by up to 80% after an hour at marathon effort.12

With less blood reaching it, your gut can't absorb as much at once. A gel taken without enough water stays concentrated, leaves your stomach more slowly, and is more likely to cause cramping, bloating or nausea.

That's why you always take water at the same time as the gel.

When you do, a gel works as well as a sports drink. A 2010 study found that athletes used the carbohydrate from gels taken with plain water just as well as the same amount of carbohydrate mixed into a drink.4

What 300 mL Looks Like on Race Day

On a race course, the water comes in aid-station cups. Volunteers fill them about halfway so the water doesn't splash, and you lose some more as you run with the cup and drink from it. A good estimate is that each cup gives you 100 mL (3.5 oz).

That means a 25-gram gel needs 3 cups of water. Take the gel with the first cup, then grab another cup or two before you leave the table.

Where to Take Each Gel So the Water Is There

Most runners plan their fueling by time, for example a gel every 30 minutes. But if there's no aid station in that 30 to 45 minute window, you'll either have to skip the gel or try to take it without water.

Take every gel where you will have water for it, at an aid station or with your own bottle in hand. Don't take one halfway between tables because the clock says it is time.

Want to see where the water is on your own race? Check out our course library, where each race guide lists its aid stations, and if your race isn't there yet, send it to us and we'll map it for free.

CarbRate's course feature puts each gel at a spot with water, which is one of the things that decide when you take each gel.

Do You Need More Water With a Gel in the Heat?

The water each gel needs stays the same on a hot day: about 300 mL (10 oz) for a 25-gram gel. What changes is how much you need to drink in between.

You sweat more in the heat, and once you fall behind on fluid, your stomach has a harder time emptying what you give it. In a 1990 study, people who had lost 4% of their body weight to dehydration emptied a carbohydrate drink from their stomach more slowly while running at 86°F (30°C) than they did when they were hydrated.5

Six of the 16 people in the study had stomach problems in that dehydrated run. Nobody reported stomach problems in the other trials.

Falling behind on fluid matters more than the temperature itself. A 1989 study found that exercising at 95°F (35°C) didn't consistently slow how fast water left the stomach, but exercising at that temperature while dehydrated did.6

That means on a hot day, the 300 mL (10 oz) with each gel is the minimum you drink. Drink at the tables between your gels as well, and count the water you take with each gel toward your total for the race.

How much more depends on how much you sweat. CarbRate works out your fluid from your sweat rate and updates the whole plan when the race-day forecast comes in.

How to Practice Taking Water With Your Gels

Drinking 300 mL (10 oz) of water every time you take a gel while running at race pace takes practice, and your stomach gets better at it the more you do it.

In a 2008 study, runners did 6 runs of 90 minutes, spaced about a week apart. From the 2nd run on, they drank enough to replace their sweat, about 1,250 mL (42 oz) per run.7 They rated their stomach comfort better on the 5th and 6th runs than on the 2nd.

The same goes for the gels themselves. In a 2017 study, runners who practiced taking carbohydrate during their runs for 2 weeks had less gut discomfort afterward, and less of the carbohydrate they took in went unabsorbed.8

To practice, take your gels with the same amount of water you plan to use on race day:

• Practice on your long runs and race-pace workouts, because race effort is when blood flow to your gut drops the most.
• If you plan to use the course water, practice drinking from a paper cup while you run.
• If you plan to carry a bottle, practice with the bottle and the gels you'll race with.

CarbRate's practice schedule builds these sessions from where your stomach is today, puts them on the runs that count, and after every rough run tells you the one thing to change next.