Pin Configuration Fresenius hemodialysis series bibag conductivity sensor

It could be a three electrode cell, or two electrode plus a temperature sensor.

However, it appears to be a high range sensor for an electrolyte solution, rather than a water purity sensor?

It could be an inductive type, in that case? If so, there would presumably be two combinations of wires that show connectivity to the coils.
That would need a totally different interface to an electrode-type cell.
One coil is driven and the other sensed. The signal level at the sense coil increases with higher conductivity.

A wet sensor with electrodes should show no connectivity between the probe wires and other connections.