Whenever you go hiking, it's important to stay properly hydrated. This is especially important in winter, when even mild dehydration can cloud your judgment and reduce your energy level.
In winter, water loss occurs through perspiration and respiration. While you can regulate your perspiration rate by slowing down your pace, most people are not even aware that they lose water through respiration.
When you exhale, your breath transports the moist warm air in your lungs to the drier air surrounding you. If you have a mustache like me, this process is very apparent from the icicles that form on it.
I always make a point to prehydrate before I go hiking. If my day hiking partner and I are driving to the mountains for a hike, we each start drinking a liter of water in the car an hour before we hit the trail.
This is especially important in winter when the rate in which you lose water can exceed the rate in which your body can absorb water.
Normally, people lose anywhere from 0.5 to 1.5 liters of water per hour when hiking strenuously. Since your body can only absorb a liter an hour, not prehydrating puts you at risk of becoming dehydrated and staying that way during a strenuous hike.
Drinking Throughout the Day
It's important that you keep drinking water regularly during a winter hike to stay properly hydrated. If you normally use a hydration system during the rest of the year, it can be difficult to adapt to its absence in winter.
I counter this by always taking a sip from one of my insulated water bottles when my hiking partner stops to catch her breath, checks her maps, adds or removes a layer, or stops to look at a bird.
Once you get into this habit, staying hydrated in winter becomes second nature.
Post Hike Hydration
One of the first things I do after a winter day hike is to drink another quart of water and eat some food. This keeps me alert when we're driving home.
If I'm backpacking in winter, I do the same thing, except we have to melt our water first. I also take a quart of hot water to bed with me and sip it when I wake up during the night to pee. Staying hydrated is important even at night because it helps the digestive processes that keep you warm after a big dinner and ensures that you don't wake up mildly dehydrated the next morning.