Hydration Planning for Race Day
Hydration mistakes run in both directions. Underdrinking is the well-known risk, but overdrinking, forcing down more fluid than your body needs, is a real and often overlooked problem that can cause its own discomfort and, in rare cases, more serious issues.
Hydration before the race
Drink normally in the days leading into a race; there's no need for dramatic overhydration the night before or morning of. A normal glass of water with breakfast, 2 to 3 hours before your start time, is generally sufficient preparation for most race distances.
How much to drink during the race
Drink to thirst at aid stations rather than forcing a fixed amount at every stop. For most recreational runners in moderate conditions, this naturally works out to roughly 150 to 250 ml every 20 minutes or so, but thirst is a more reliable guide than a fixed formula for most people.
Adjusting for heat and humidity
In hot or humid conditions, sweat rate increases significantly, and an electrolyte drink at aid stations, where available, helps replace lost sodium in a way plain water alone doesn't. If you're racing in a notably humid city, such as Mumbai or Chennai, pay closer attention to hydration than you would training in a drier climate, since humidity can mask how much you're actually sweating.
Warning signs to watch for
Dizziness, unusual fatigue beyond normal race effort, or a headache during a race can be signs of either under or overhydration, and it's not always obvious which without more information. If you experience these, slow down, seek out medical support along the course if it doesn't resolve, and don't push through symptoms hoping they'll pass.
Should you carry your own water?
For a 5K or 10K with frequent aid stations, carrying your own water usually isn't necessary. For a half marathon or marathon, particularly in hot conditions or on a course with wider aid station spacing, many runners carry a small handheld bottle or hydration belt as a supplement, not a replacement, for aid station water.
See race-day nutrition basics and check your event's aid station details before race day.
Read race-day nutrition guideAid station spacing varies more between events on the platform than most runners expect, and it's one of the details worth actually reading on the category page rather than assuming. My honest take: if you're racing somewhere genuinely humid for the first time, don't rely on your usual hydration habits from home. Check the specific event's aid station intervals and plan accordingly, since a gap that felt fine in a dry, cool city can catch you out somewhere hotter and more humid.
Frequently asked questions
How much water should I drink during a half marathon?
There's no single fixed amount; drinking to thirst at aid stations works well for most recreational runners, typically translating to small amounts every 20 minutes or so.
Is it possible to drink too much water during a race?
Yes, overdrinking is a real risk and can cause discomfort or, in rare cases, more serious issues. Drink to thirst rather than forcing a large fixed amount at every stop.
Do I need electrolyte drinks or is water enough?
For shorter distances in mild conditions, water is usually enough. For longer distances or hot, humid conditions, an electrolyte drink at aid stations helps replace lost sodium more effectively.