Answer:
Environmentalists want to keep this from drying.
It is in every mountain, it's not in any hill, it's not in all the world, and yet it's in the mill.
I'm the son of water but when I return to water I die. Who am I?
There is one in every corner and two in every room.
What get's more wet while it dries?
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.