Last week one of the Knox caretakers noticed a small leak in one of the valves in the water pipes. He tried to tighten the valve to stop the leak. This caused the 100 year old pipe to weaken and burst causing the full force of water pressure to come pouring in to the lower theatre.
The plumber was called to shut off the water, but the shut off valve was buried in a wall so there was a bit of destruction involved to find it.
This pipe would have weakened and burst anyhow, so really it was a good thing that this happened during the week when people were around.
And here is the aftermath. Baby waterbots cleaning up the mess.