One symptom of the flu is a high fever, which can lead to sweating. You might also be dealing with bouts of vomiting or diarrhea. Your body needs plenty of fluids to replace lost liquids, and even more to fight off the infection.
Water is best, but you can also drink herbal teas or tea with honey. These can have a soothing effect on your symptoms while keeping you hydrated. Two things you should always avoid, though, are alcohol and caffeine.