How to stay hydrated

  • By
    Roxanne Fisher - Health editor -

Staying fully hydrated can be a challenge, especially for those who are training hard for an event like a marathon. We asked sports nutritionist, James Collins some of your most commonly asked questions...

How to stay hydrated

Question 1:

What are the different strategies for staying hydrated during a marathon?

James says:Hydration strategies
This is often a contentious issue, and ultimately takes some planning and a bit of common sense. The overall goal of the hydration strategy is to replace the body's water and electrolytes that are lost through sweat.

A fluid loss greater than 2% of body mass (e.g. 1kg for a 50kg runner) can have a negative affect on performance and can increase the strain on the body. Over hydration can also be a problem in long races like a marathon. Recreational runners drinking large amounts of water at each opportunity can lead to 'hyponatremia' (a dilution of blood electrolytes), which can have serious consequences.

During training, runners should attempt to estimate sweat rates. This is easily done by weighing themselves (in minimal clothing) before and after a run (following towelling down), then subtracting any fluid consumed. Every 1 kg lost is roughly equal to 1 litre in sweat . For example, 1 litre lost from a two hour run would equal a sweat rate of 500ml per hour.

Note: This estimation should then be repeated in hot temperatures as sweat rates can vary greatly in hot conditions.

Once this has been worked out, a basic strategy can then be formed to reduce dehydration during the race. Alongside this, runners should fundamentally listen to their body, and drink according to thirst. The body's physiology is tightly regulated so that when there is excessive sweat loss (affecting blood levels) the thirst mechanism is triggered.

Both of these measures can help runners develop an appropriate strategy to stay hydrated - one size doesn't fit all.

Question 2:

How often should I drink during a run?

James says:How much to drink
Make sure you start your race fully hydrated. Drinking approximately 500ml of water two hours before the race should suffice. This will allow any excess to be passed as urine before the starting pistol.

Just before the start, plan to drink a small amount (about 150ml). During your run, drinking should match sweat losses as closely as possible, taking care not to over hydrate. 150-250ml fluids every two miles might be a good starting point.

Question 3:

What are electrolytes and where can I get them?

James says:runner
Electrolytes are found in the blood, sweat and other bodily fluids and have an important role in maintaining fluid balance within the body. Sodium is the most important electrolyte for hydration, while others include potassium and chloride. Sodium levels in the blood are tightly controlled. Fluid and electrolytes are lost in sweat and therefore need to be replaced. Sodium allows the body to absorb and retain more fluid, thus maintaining hydration. Drinking large volumes of water alone can just pass through you and be lost as urine.

You can top up your sodium levels with sports drinks and gels, which are an easy way to absorb and retain fluid during a long run or race.

Question 4:

Can I just drink water during a marathon, as I don't like sports drinks?

James says:Electrolytes
If you prefer, you can base your hydration strategy around water earlier in the race. It is, however, advised to consume electrolytes, from available sports drinks or gels, especially if it is hot on the day.

Try out sports drinks or gels during training to see if you can find one that works for you. During an event, try consuming sports drinks at the drinking stations on route - you could rinse your mouth out or have a mint after if it's the taste you don't like. If you're running in the London Marathon, their website will tell you what products will be available from drinking stations on the day.

Question 5:

Can I continue to drink alcohol in moderation leading up to a race or is it better to cut them out altogether?

James says:alcohol
It's better to cut out (or at least cut down on) alcohol consumption leading into an event, as it can interfere with the body's maintenance of blood glucose and recovery (including sleep quality) after training. If you really can't resist the odd tipple, ensure that you drink after you have fully recovered following your last run.

Are you training for an event this year? Share your tips and experiences below.


As a sport and exercise nutritionist, James Collins regularly provides comment and consultation within the media and maintains a role of governance within Health & Nutrition in the UK, where he sits on The Royal Society of Medicine's (RSM) 'Food and Health' Council. He was heavily involved in advising Team GB in the run up to the London 2012 Olympic games, and now towards Rio 2016.

All health content on is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact  your local health care provider. See our website terms and conditions for more information.

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