People say that it is good to drink 8-10 glasses of water a day. This is a good, general rule for an average sized person, according to medical authorities. However, it is not a dictate: every particular person needs to find their own needful intake, depending on their individual body, their level and type of activity, and other food/drink consumption. Dry skin, which manifests itself most rapidly on the extremities (cracked skin on hands and on heels are often concerns), and on the lips (because more air passes by the lips during breathing and speech, accentuating the effects of dry air) are exactly the symptoms that should be monitored to determine sufficient hydration. People have a variety of "cures" for such symptoms, including chapstick for the lips, and various balms and oils and butters for the skin. Such "cures" can help reduce the evaporation losses in those particular areas by isolating them from the dry air, but then one loses the symptoms available to determine adequate hydration. I personally know of several people that have gone to the emergency room in recent years, and the diagnosis there was dehydration, and they wound up with a big bill for a saline drip administered by a nurse at the emergency room rather than a small increase in their water bill. Such an expense is significantly higher than bottled water, even, which is another amazing marketing success which unnecessarily parts people from their money in smaller amounts but more frequent intervals than emergency rooms, and except in unusual circumstances is no higher quality than tap water.
It is harder for many people to achieve good hydration in the winter, because the effects of perspiration (that hot, sweaty feeling) are reduced. However, due to the dry air (science tells us cold air cannot hold as much humidity as warm air, and warm air from a furnace is basically cold, dry air warmed up, so it is warm, dry air unless an effective humidifier is used to add humidity), perspiration actually happens faster in the winter, just like it does out here in the semi-desert, but is less noticed because of the dryness of the air, which causes the perspiration to evaporate rapidly. So if 8-10 glasses of water keep you hydrated in the summer, you need to increase it in the winter, even though you don't feel hot and sweaty (which are symptoms that cause people to resort to a nice, cold drink). Also, there is a tendency in the winter (perhaps not for you), to drink more warm drinks such as coffee and tea, which are diuretics (things that help remove water from the body) because they are warm, without realizing that means that water intake should be increased even further, because they are diuretics.