During the summer months, sweating and sunshine can lead to dehydration, but just because it's cold out doesn't mean your not at risk.
Household heating reduces the humidity in your home. We can lose 1-2 liters of water a day just from breathing. According to the Mayo Clinic, "Having a cold or sore throat makes you more susceptible to dehydration because you're less likely to feel like eating or drinking when you're sick. A fever increases dehydration even more.