Yotty, The water detector is an inverted ultrasonic fuel probe which looks for the water/fuel interface, and is fitted at the inboard (lowest) end of the tank. If the water in the fuel didn't make it to the water detector, having frozen first, or was so much that the water detector was fully submerged (from what I remember, its only about 6 inches tall), then perhaps it wouldn't have shown up on the maintenance log?