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Stay Hydrated in the Winter Months
From www.hprc-online.org

Most people associate dehydration with hot weather, but you can get dehydrated in cold weather too. It isn't always easy to get the fluids you need, especially when you're on a mission. If you're active outside for less than 2 hours, your risk for getting dehydrated is probably pretty low. But if you're out in the cold for hours or even days, the combination of heavy clothing and high-intensity activity that makes you sweat could lead to dehydration.
Dehydration happens in cold weather for a number of reasons. Cold weather tends to move blood and other body fluids from your arms and legs to your core, increasing your urine output. Cold weather also decreases your body's thirst sensation, which is normally an early sign of mild dehydration. Other signs of dehydration include headache, dry mouth, fatigue, muscle cramps, constipation, dry skin, and feeling dizzy or light-headed.
One way to see how hydrated you are is to check the color and amount of your urine. (Snow makes a good test spot.) Dark urine in smaller amounts than usual indicates dehydration. Ideally, your urine should be light yellow.
Water and sports drinks are the best fluids to help you stay hydrated, even in cold weather. Energy drinks can have diuretic effects, dehydrating your body, so avoid using them as a substitute for water or sports drinks. Also avoid drinking alcohol in cold weather. It might make you feel warm initially, but it can reduce your body's ability to retain heat.
When you exercise in the cold, don't rely on thirst to tell you when you need to drink. Drink often and before you're thirsty. You should take in 3 to 6 quarts of fluid per day (including what's in your food) during cold-weather training and operations.
Make sure to take in enough electrolytes (minerals in your blood such as sodium and potassium) if you'll be out for more than 2 hours. Drinking too much plain water can cause hyponatremia (low sodium levels in your blood), which can result in severe brain damage or death.