Plot hole: There are numerous problems with the final solution to putting out multiple burning floors of a skyscraper by blowing the water tanks under the roof. Blowing the floor under the tanks only channels the water into the Promanade Room. From there it cascades out the windows and - as we see in the film - falls to the ground without touching the fires on the lower floors. A tiny percentage makes it into the stairwell door and elevator shaft, despite the fact that the elevator doors were closed. All of the stairwell and elevator doors in the building were shut; none of this water makes it to the fire. Also, as we see the flames going out from all the floors no water is coming out of any of those windows, proving that the fires are going out without any water.
Plot hole: The roof of the building is fully engulfed in flames (from the helicopter explosion) right up to the point where they blow the water tanks. When they explode the water tanks the whole building is put out. It would have been impossible for the water tanks to put out the roof fire; it was above the tanks. Although all of the building shots at the end of the film are looking up at the structure you can see flames shooting off the roof before the tank explosions, then no roof flames whatsoever after.
Plot hole: By the time O'Halloran phones Roberts, who is in the promenade room, and tells him of their plan to blow the water tanks, over 50 of the floors below the promenade room, along with the roof which is also ablaze, have been destroyed by the fire. So surely the phone lines would have been destroyed as well, making a phone call to the promenade room impossible.