Answer:
What do you call a pig that is no fun to be around?
What goes through cities and fields but never moves?
I start new then become old. Start clean but be one dirty. I usually start big then become little.
No matter how little or how much you use me, you change me every month.
A necessity to some, a treasure to many, I'm best enjoyed among pleasant company. Some like me hot, some like me cold. Some prefer mild, some like me bold. What am I?
Give it food and it will live, give it water and it will die.