Keeping hydrated is just as important in the winter months.
Replace What You Lose
H2O leaves the body through exhalation, perspiration, and urination. If your urine is pale, you are well-hydrated.  Alternatively, if it’s dark, you need to drink more fluids.
Eat Fruit
Don’t stop eating fruit during the winter months, they are an excellent source of water:  Christmas clementines are 87% water, apples 84% water and pears are 84% water.
Soup
Soup is warming and hydrating.  Here are some winter ideas: tomato, pumpkin and ginger, butternut squash and chilli, or minestrone.
Drink Hot Chocolate
Hot chocolate provides a good carbohydrates-to-protein ratio, ideal for a post exercise recovery drink.  Maybe hold the cream!
Limit Alcohol and Caffeine
Caffeine and alcohol have diuretic effects. Save them for after your cold-weather walk.