I have not flown the machines, but did get involved in the accident investigation of a crash in Romania that killed 6 British tourists.
The only plausible explanation for the crash was that the fuel sample that was taken was done with the aircraft in a 5 to 7 degree nose down (estimated) attitude, due to the slope where it was staying. The fuel sample showed no water, but the engine failed shortly after the aircraft started to decelerate and descend (i.e. when the nose came up).
Moral - make sure you keep the helicopter (all helicopters) on a level surface if you want to make sure you get the water to go to the sump.
The otherwise reliable engine had stopped prior to the aircraft hitting the ground...