Marathon running is often regarded as the pinnacle of long-distance running. Although there are now even longer ultra-marathons for elite runners, the traditional 26-mile run is still thought to be the greatest bucket-list challenge for those that want to push themselves to their limits.

staying hydrated during a marathonIt is a severe mental and physical test, where success is far from guaranteed.

Preparation for a marathon is of paramount importance. You really have to start training a long time before the event and regularly so. Another hugely important and all-too-often overlooked ingredient for a successful run is nutrition

But perhaps the most indispensable and immediately damaging to performance is hydration. If you get your hydration plan wrong before and during a run, particularly long distance marathons, you are entering a world of pain, where failure is certain.

Here we talk you through the importance of staying hydrated and how you can ensure you do so.

Let’s start by looking at what happens if you don’t drink enough


The most obvious problem of a lack of fluids in your body is dehydration. You can suspect that you are dehydrated if you feel dizzy, lightheaded, thirsty and your pee is darker in colour and you are peeing less. In more severe cases you may get a painful headache, faint, have very dry lips, feel nauseous and very unwell. 

Generally speaking, we need about 3 litres of water a day to stay adequately hydrated. However, if you are exercising or running for more than 45 minutes which involves sweating, you need to take on more fluids.

Yet, if you drink too much, you may also face problems.

rich gill running a trail marathon with water bottles in running vest



Sodium levels are critical to your bodily functions. A healthy level of sodium is 135-145 mmol per litre. What many runners get wrong is to increase their fluid intake too much and actually dilute their sodium levels. As a result, they may be opening themselves up to a range of unwanted performance-weakening symptoms such as nausea, cramps, fatigue and headaches.

Many runners believe that having clear urine is a good way of checking to see that they are not dehydrated and so they use the ‘more is better’ approach to fluid intake. In recent years, however, there have been many cases of athletes over-hydrating and suffering from Hyponatremia, which is equally damaging to their performance (and health) as dehydration.

So, it is a bit of a balancing act that requires a little consideration to get right.

How to stay hydrated before, during and after a marathon

Although water is obviously the go-to source for staying hydrated, it may not be the best and only choice for those taking on a marathon. Please don’t misunderstand us, water is extremely important and a key part of the hydration plan, but there are other performance and hydration-enhancing fluids, gels and tablets which can assist you in your running endeavours. Sports science has evolved dramatically and it is now extremely rare to find an athlete who does not include these in their hydration plan. Furthermore, only drinking water during a long-distance running event can lead to sloshy-belly discomfort and, as mentioned before, hyponatremia. 

How to start a marathon hydrated

Your sports hydration plan starts long before the marathon itself. To understand what your body needs you must test it. This means checking how much you sweat during exercise. A good way to do this is to weigh yourself before and after a long run (at least 1 hour). For every pound (0.4kg) you lose in weight you should be aiming to rehydrate with approximately 0.5kg (20-24 ounces) of water. A bit over half a litre basically. 

So if you sweat heavily and lose 1kg over a 2 hour run, you need to be supplying your body with about 1.2kgs (40oz) of water. That's just over a litre. 

rich gill starting a marathon happy and hydratedOnce you’ve understood your sweat rate, you can start looking at ways of maintaining a good hydration level.

Before the marathon itself, all runners should be aiming to drink about ½ litre of water about 2 hours before the run, alongside some food. Then around 15 minutes from the start have a further glass of water (about 6oz). 

This is also a good time to start feeding your body electrolytes via a sports hydration drink or hydration tablets. Both of these will quickly add all-important electrolytes and potassium, sodium and magnesium which help maintain and regulate a wide variety of bodily functions including hydration.

How should I hydrate during a marathon? 

  • Water
  • Sports hydration drinks
  • Hydration tablets
  • Gels

The best approach is to sip regularly rather than drink a lot in one go. This is to avoid getting sloshy-belly and over-diluting sodium levels. Again the amount depends on your sweat rate, but we can say that you'll need to take on about a ⅓ of a litre every 15 minutes if you sweat a lot. 

rich gill on track staying hydrated

These days, though, there are sports drinks and gels which can and should be consumed over long-distance runs or marathons. Sports drinks, or powders which you can add to your water, contain electrolytes. Electrolytes are essential for keeping bodily systems functioning efficiently. They are responsible for maintaining and regulating nerve and muscle functions, hydrating the body quickly, balancing blood acidity and helping rebuild damaged tissue.

There are also hydration tablets which can be easily eaten as you go. These tablets add potassium, sodium and magnesium which are lost through sweat. They also contain bicarbonate which can reduce stomach acidity which means your body can absorb the electrolytes quickly. 

Additionally, sports gels are now a common practice amongst marathon and long-distance runners. These add much needed energy (carbs) to keep the body running smoothly.

So, during a marathon you can take a bottle of water and add a satchel of electrolytes to it and sip as you go. Pair this with a sports gel to keep you going.

styrkr electrolytes hydration powder

This could be a practical discomfort if you are running with water bottles in both your hands so investing in a running hydration vest (a lightweight jacket with pockets for water bottles and straws) is probably a good idea. Also, it allows you to have a bottle for water and a bottle containing a sports drink high in electrolytes.

How to rehydrate properly after a marathon

Once the marathon is over (well done), you should still be giving your body fluids to help rehydrate properly. Again, it is a good idea to weigh yourself to see how much weight you have lost over the run.  For every pound (0.4kg) you lose in weight you should be aiming to rehydrate with approximately 0.5kg (20-24 ounces) of water. Alternatively, sports drinks or hydration tablets can provide the body with what it needs too. 

Another essential thing is of course food. You may not feel hungry after such a physically exhausting challenge but you should try to eat some carbohydrates such as bananas, peanut butter and jam sandwiches, fruit or yoghurt. 

Then, have a reward meal later on and rest up for a few days. You deserve it.

rich gill celebrating a successful ultra marathon win

3 takeaway tips to stay hydrated

  1. Know your sweat rate and calculate what your hydration needs are.

  2. Use sports drinks, hydration tablets and gels to add much needed electrolytes and carbs before and during the event, invest in a hydration vest to assist you practically.

  3. Rehydrate after the event by measuring your weight and replenishing with liquids accordingly.

styrkr free fuel tool for sports nutrition
Image credit: @rich.trails