How is it We Find Water to Fight the Fire, but None to Prevent it?

    I continue to wonder why we don't keep the foliage wet to avert forest fires. I would guess it is not the trees, themselves, that need to be wet, but the foliage around them. If the foliage is dry, it catches a spark and is set on fire. But, if you water it enough to keep it green, a good portion of our forest fires would never happen.
   I wonder why we don't airlift water to some spots. Maybe, in some cases, even install waterlines just beneath the forest surface. I've been told, all the water in our lakes and reservoirs is spoken for, so we can't water our forests. I wonder, though. If all our water is taken, how do we come up with some when the fire breaks out. How is it we can find water to fight the fire, but cannot find any to prevent it?