How to put out fires without waves

I started out with ground zero and expanded on the sectors from there, Ignoring that the frozen forest had popped up. Now, there are some air units that start a fire when theyre put down and i have no idea how to put them out as i cant obtain water in any way i know. Also, the player unit doesnt seem to be able to pick up water like it can with other resources. So how can i put out these fires? And if i cant, is it okay to leave a sector that is under attack and go on and focus on frozen forest to unlock the craters?