I’ve lost count of how many times I’ve returned from a freezing ride only to realize my water bottles were still full. I assumed I just wasn't working hard. I was wrong. I didn’t realize how serious winter dehydration was until I heard about a cyclist who ended up in the emergency room with dangerously low blood pressure after a sub-freezing 50-mile ride, not because he crashed, but because he simply forgot to drink.
Winter hydration matters more than you think
If I’m being honest, I would say that hydration doesn’t feel as important in the winter, but it actually is. In the summer months, you can see and feel the sweat dripping off your body, the heat from the sun helps you recognize your need for hydration.
But in winter, you don’t feel as thirsty. You might not feel the sweat, and you don’t realize how the cold, dry air pulls moisture from your body. And likely, the discomfort from feeling cold is yelling much louder in your brain than your body’s cry for hydration.
But it’s just as easy – if not easier – to get dehydrated when cycling in the winter as it is in the summer.
Hydration in cold: What changes in your body
Cold weather doesn’t turn off your risk for dehydration, but it does muffle your body’s internal alarm system.
This process begins with peripheral vasoconstriction, where your blood vessels contract in your limbs to move blood toward your core to protect vital organs. Unfortunately, your body misinterprets this sudden shift as an excess of total fluid. In an effort to balance the system, it responds by dumping water and sodium through a process known as cold-induced diuresis. This is why you may find yourself urinating more frequently in the cold than you do in temperate weather, even if you haven't increased your intake.
Beyond fluid shifts, the cold actively blunts the sensation of thirst. Cold exposure can reduce the drive to drink by as much as 40 percent, even when the body is already in a state of dehydration, according to this research published in the Medicine and Science in Sports and Exercise journal.
Simultaneously, the dry nature of winter air forces your body to work harder to humidify every breath. As your breathing rate climbs during exertion, you lose significant amounts of water vapour through your lungs.
While you might not feel as drenched as you would on a humid summer day, your heart is actually working harder to circulate blood through constricted vessels, and sweat is often evaporating instantly into the dry air or becoming trapped in heavy layers of clothing.
Common winter dehydration symptoms for cyclists
Dehydration symptoms can be surprisingly subtle, so here’s what to look for on the bike:
HR drift: heart rate climbs at the same power/effort; you feel like you’re working harder than the numbers suggest
Early fatigue (heavy legs) and fading sooner than expected
Dry mouth, dry lips, scratchy throat
Headache starting mid-ride
Lightheadedness when you stop, stand, or start again
Poor focus, brain fog and/or irritability
After the ride, you may notice:
Dark urine and/or peeing less than usual later
Headache and unusual tiredness
Dry skin, or persistent dry mouth
Crampy feelings
Even minor dehydration, a loss of less than 2 percent of your body weight, can make thermoregulation more difficult and cause cognitive issues. Recovery is harder and you might finish a ride feeling extra zapped, with more headache, irritability, and next-day heaviness.
When to take it seriously
Seek urgent help if you have confusion, fainting, inability to keep fluids down, or very little/no urination, since dehydration can become dangerous.
Winter dehydration facts athletes often overlook
Understanding the biology of the cold is only half the battle, as several environmental and behavioural factors can cause dehydration to snowball during the off-season.
Many athletes unknowingly begin their sessions in a state of “pre-dehydration." Because the urge to drink is lower in the winter, it’s common to start a workout with low fluid levels, making it nearly impossible to catch up once the effort begins.
However, it is equally important to avoid the trap of over-correcting; during long, low-intensity rides, drinking excessive amounts of plain water without electrolytes can lead to exercise-associated hyponatremia, which is when the level of sodium in your blood is lower than normal.
Balancing your intake by planning fluids ahead of (without relying on thirst) is the only way to ensure that "winter legs" aren't actually just a symptom of a shrinking blood volume.
How to stay hydrated in winter: Daily habits
Since it’s common for athletes to be chronically dehydrated, one way to prevent this is by following good daily hydration habits.
First, find your daily baseline. For example, many people find they need between 2.7 and 3.7 litres per day (including liquid and water from food intake), according to the Mayo Clinic. If you’re doing any training or heavy sweating, you might need to add more.
Don’t just rely on feeling thirsty, because in the winter, you might not feel thirsty at all. Try to spread your drinks throughout the day. For example, have a drink with every meal and one in between or with snacks.
Check the colour of your urine once or twice per day for a quick reality check of how you are doing. You should aim for pale yellow most of the time. Darker yellow usually means “drink more.” (Keep in mind, it's naturally darker first thing in the morning, so don’t forget to check later on.)
You don’t have to just drink water. Warm fluids count too, and they might be easier to drink when it’s cold. Herbal tea, broth, warm water with lemon, and decaffeinated coffee are all helpful choices. Total fluid intake matters, not just plain water.
Eat some of your hydration. Foods count, too! Water-rich foods – such as soups, oatmeal, yogurt, oranges, grapes and cucumbers – all help you get to your daily hydration goal.
Add electrolytes strategically. For most people, your water and food intake will cover your daily electrolyte needs, but if you’re doing longer or harder rides, you’re sweating a lot, or drinking plain water makes you feel washed out, you might want to add in some electrolytes.
Winter hydration tips for cyclists and endurance athletes
Be proactive and take your hydration seriously. One way to check is to occasionally weigh yourself before and after workouts so you know how much fluid you’re actually losing. If you’re losing more than 2 percent of your body weight during a workout, you’ll want to be extra diligent.
Start your ride already hydrated. Make sure you drink a glass of water with breakfast so you aren’t trying to catch up mid-ride. During the ride, you might want to sip on a schedule, such as every 10 to 15 minutes, because thirst is an unreliable indicator in the cold.
Using a winter hydration pack and bottles in cold conditions
It can be challenging to keep your water or sports drink from freezing in cold conditions.
Insulated bottles can keep your water from freezing longer. Fill them with warm water or tea to help warm you up as you drink.
Friends of mine showed me how they keep their bottles in their jersey pockets so body heat can keep them from freezing. If your bottles don’t fit in your jersey pocket, you may want to turn them upside down in your bottle cages to prevent the nipple from freezing for as long as possible. This works because water freezes from the top down, so the ice plug will start at the “bottom” of the bottle, rather than the part you drink from.
My mountain biking friends ride with a Camelback hydration system. They tuck it up under their jacket, so it stays a little bit warmer. And if you’re really desperate to keep your water warm, try sticking disposable hand or foot warmers up against your hydration system for added heat.
Indoor training, sweat loss and hidden dehydration
Indoor cycling is a different animal. That growing puddle beneath your trainer or smart bike isn't just a badge of honour; it’s a warning. Because you lack the natural evaporative cooling of the wind, indoor sessions are prime territory for "hidden dehydration," stripping your fluids much faster than a ride outdoors.
When you ride outside, the speed of your movement creates airflow that helps evaporate your sweat and cool you down. Without that airflow, your body doesn’t cool efficiently, so you sweat earlier and more often. With your indoor cycling setup, you need to add airflow (such as a fan or blower) to get similar sweat evaporation.
If you see puddles below you, that means you’re sweating a lot and it isn’t evaporating. If you have a big fan, you may be evaporating sweat fast enough to prevent puddles, but you’re still losing the same amount of fluid from your body.
Sweat rates vary wildly, but “typical” exercise sweat rates are often reported around 0.5-2.0 L/hour, and some athletes go even higher, according to this study published in Nutrients. That means a 75- to 90-minute ride on the ROUVY indoor cycling app can quietly cost 1-3+ litres, more than you can easily replace in that time frame.
Similar to outdoor symptoms, there will be signs that you’re getting dehydrated on the trainer. For example:
Your heart rate climbs higher at the same power output.
Your rate of perceived exertion may feel much worse (“Why does Zone 2 feel like Zone 3?”).
You may be thirsty, have a headache during or after, feel irritable or lose that “snap” when you’re trying to hit your intervals.
You may notice darker urine after your ride.
Tips for managing hydration when riding indoors
Start with a strong fan to keep you from overheating.
Drink on a schedule (for example, a few big sips every 15 to 20 minutes).
Add in electrolytes or sodium, especially if you notice salt on your kit or you’re sweating heavily.
Don’t forget to rehydrate after your ride, too.
