So, if this were possible (a plane would dump water over a swathe of old Paris, a helicopter would be necessary) to dump a "giant cup of water" on the flames, it would be a sufficient volume and force to knock the walls down. Destroying the building in order to save it is not the goal of fire fighters.
So horrible to watch the massive fire at Notre Dame Cathedral in Paris. Perhaps flying water tankers could be used to put it out. Must act quickly!— Donald J. Trump (@realDonaldTrump) April 15, 2019
Hundreds of firemen of the Paris Fire Brigade are doing everything they can to bring the terrible #NotreDame fire under control. All means are being used, except for water-bombing aircrafts which, if used, could lead to the collapse of the entire structure of the cathedral.— Sécurité Civile Fr (@SecCivileFrance) April 15, 2019