How to Prepare Your Hydration for a Hot Race
When race day is approaching, it can be tempting to check the weather forecast and decide your hydration strategy the night before.
In reality, the most useful preparation starts much earlier.
Running in hot conditions increases thermal stress and can increase fluid losses through sweat. But that does not mean every runner should follow the same rule for water, electrolytes or salt. Hydration needs vary according to factors such as exercise duration and intensity, acclimatisation, humidity, sun exposure and individual characteristics.
That is why preparing for a hot race should not start with a universal formula.
It should start with a few practical questions.
1. What will actually be available at the aid stations?
Before deciding what to carry, first understand what the organiser will provide.
Knowing that “there will be aid stations” is not enough. Check:
- where the aid stations are located;
- approximately how many kilometres there are between them;
- whether they provide only water or other drinks as well;
- whether you need to carry your own cup, flask or bottle;
- whether additional water points may be introduced in hot conditions;
- whether the race is self-supported or semi-self-supported.
This information can completely change what you need to carry.
The Lisbon Eco Marathon 2027, for example, currently lists different aid-station locations depending on the distance. For the marathon, stations are planned around km 4, 10, 16, 22, 28 and 36, as well as at the finish, while the half marathon lists stations around km 4, 10 and 15 plus the finish.
Other events work very differently.
At the V Trail Vilarinho Cima 2027, participants are expected to carry their own cup because disposable cups are not provided at the aid stations.
And the III Mini-Trail Santoinho is organised in semi-autonomy, meaning runners need to carry the fluids and nutrition they expect to need during the course.
These are not necessarily examples of extreme-heat races. They illustrate a broader rule:
never assume how an aid station works — check.
2. Check organiser updates again before race day
The regulations you read when you registered may not contain the final information.
When hot conditions are expected, organisers may adjust start times, reinforce aid stations, add extra water points or issue specific recommendations for participants.
During race week, check:
organiser emails → race regulations → official event page → social media → information provided with bib collection
And pay particular attention to last-minute updates.
It is also worth checking the event page again on RaceFinder before travelling to the race, as information such as start times, aid stations, mandatory equipment and other instructions may be updated when new details are released by the organiser.
3. Do not discover your hydration strategy on race day
Runners often have very different experiences with hydration.
One runner may feel comfortable completing a certain training distance with very little fluid, while another may need to drink regularly over the same distance, especially in warmer weather.
That does not mean one strategy is correct and the other is wrong.
It means hydration is individual.
If you expect warm conditions during your target race, use training to learn how you respond.
The purpose is not to turn every session into an extreme simulation of race day. It is to answer practical questions such as:
- Are you comfortable drinking while running?
- Which bottle, flask or hydration system works best for you?
- Can you drink at an aid station without stopping completely?
- How does your stomach respond?
- Will you need to carry extra water between stations?
- Does your strategy still feel comfortable after 60, 90 or more minutes?
- How does your perceived effort change when the temperature rises?
Training is not only about fitness. It is also where you test the logistics that will eventually become part of your race plan.
4. Rehearse the logistics, not just the running
A good race-preparation session should test more than your legs.
It should test the process.
Imagine you are preparing for a half marathon with water available around kilometres 5, 10 and 15.
During a long training run, you could practise a similar structure and see whether that spacing feels comfortable, whether you would prefer to carry additional fluid and how easily you can drink while moving.
For trail races and ultras, this becomes even more important.
The Backyard Ultra Ansião 2027, for example, follows the Backyard format of repeated 6.706 km loops starting every hour. In a race that may continue for many hours, understanding how the support area works and planning when to drink and eat becomes part of the race strategy itself.
The same basic questions apply to almost every event:
Where will I drink? What will be available? What do I need to carry? And have I already tested this before race day?
5. Do not copy someone else’s hydration plan
One of the easiest mistakes is to adopt another runner’s routine as your own.
“I drink this much every hour.”
“I always take this amount of electrolytes.”
“I never drink during a 10K.”
None of those statements tells you what you need.
Sweat rate and fluid losses can vary considerably between athletes, even when two runners are completing the same race at a similar pace.
Two runners of similar weight, pace and ability can therefore experience the same conditions very differently.
Use training to collect information about yourself instead of turning someone else’s strategy into a fixed rule.
6. What about electrolytes?
This is another area where a universal formula is not particularly useful.
Sweating results in the loss of both water and electrolytes, but the amount lost varies between individuals.
During longer races or particularly hot conditions, electrolyte intake may deserve more attention than it would during a short and easy session.
That still does not mean every runner needs the same amount of sodium or the same type of sports drink.
If you are preparing for a marathon, ultra-distance event or a long trail race, or if you know that you sweat heavily, this may be worth discussing with a sports dietitian, sports doctor or another qualified professional.
7. Useful questions to ask a qualified professional
Instead of simply asking:
“How much should I drink?”
give them some context.
Useful questions might include:
- “I am preparing for a half marathon that may take place in hot weather. How can I assess my individual hydration needs?”
- “I sweat heavily during long runs. Should I also consider electrolyte losses?”
- “What signs should I monitor during training to know whether my strategy needs adjusting?”
- “How should I adapt my race plan if race day is much hotter or more humid than my training conditions?”
- “I take medication or have a medical condition. Is there anything about exercising in the heat that I should discuss with my doctor?”
The last question is particularly important because some medical conditions and medications may affect how the body responds to heat.
8. Your pace may need to change too
Hydration cannot solve every problem caused by hot conditions.
On a particularly warm day, trying to reproduce exactly the same pace you ran in cool weather may require considerably more effort.
Your body has to maintain exercise while also dissipating heat. When conditions are hot — particularly when humidity is also high — that process becomes more difficult.
That means your race strategy should include the possibility of adjusting your effort.
There is no universal number of seconds per kilometre that every runner should add.
Instead, consider:
- the conditions on the day;
- how you responded during training;
- your race distance;
- your goal;
- how you feel during the opening kilometres.
Sometimes the most important pacing decision happens before you cross the start line.
9. Know when it is no longer about performance
At some point, the priority stops being pace and becomes safety.
Feeling faint, unusually weak, dizzy, nauseous, confused or significantly unwell during exercise in the heat should not simply be treated as part of “pushing through”.
If you feel unwell, slow down or stop, move to a cooler area when possible and seek assistance.
Confusion, collapse, major changes in mental state or suspected heat stroke require urgent medical attention.
No pace target or personal best is worth ignoring serious warning signs.
Hot-Race Preparation Checklist
During race week, you should ideally be confirming a strategy rather than inventing one.
Check:
- the latest weather forecast;
- organiser updates;
- start time;
- aid-station locations;
- what drinks will be available;
- whether you need your own cup or bottle;
- whether carrying additional water is allowed or recommended;
- whether you have already practised your hydration plan;
- clothing and equipment;
- whether your pace may need adjusting;
- where medical assistance will be available.
And most importantly:
do not turn race day into an experiment.
Your hydration strategy should be something you have already practised and can adapt to the actual conditions.
The Race Is Part of the Plan
Preparing for hot conditions starts long before checking the weather forecast the night before.
When choosing your next race on RaceFinder, look beyond the distance and elevation profile.
Check the:
- aid stations;
- start time;
- mandatory equipment;
- race regulations;
- level of self-sufficiency required.
Then use that information to make some of your training more specific to what you will actually experience.
A road marathon such as the Lisbon Eco Marathon may provide several organised aid stations along the route.
A trail race may require runners to carry their own cup or water supply.
A Backyard Ultra may require you to manage hydration and nutrition repeatedly for many hours.
So instead of asking only:
“How much should I drink?”
ask:
“What race am I doing, what conditions am I likely to face, what support will be available, and what strategy have I already tested?”
That is a much better place to start.
