Engineering study of the collapse
I don't know if anyone is certain about the fire suppression systems in the WTC. I suspect the water lines were severed by the impact but we may never know for sure since very few people above the impact sites survived.
Here's an engineering study about the causes of the collapse. Sobering reading.
This article from USC suggests that the sprinklers probably failed, but even if they hadn't, they probably wouldn't have been enough to put out the extensive fires from about 10,000 gallons of jet fuel and all of the interior furnishings in the buildings.