Dry mouth is not a good indication of dehydration. That can be caused by other things including the HVAC system, in combination with the naturally decreased humidity of cold winter temps. I personally often prefer outside humidity and fresh air over the surprisingly unfresh and low humidity inside air. Sugar free gum or hard candy should help. A hard candy can last a long time if you arent actively trying to work it smaller.
For judging dehydration, pay attention to urine color and frequency. Overhydration would make you go 2-3 times per hour, and it would be clear as water if you haven't taken any vitamins. It's not quite a harmful amount of hydration, so you might try to reach that point, and back off from there.