Vauxhall:
But I couldn't find on Google.
That probably tells you something.
Having said that, there are approximately a billion washing machines on the planet, each with at least one water level device, but I guess they still do it on air pressure, not water. They are cheap reliable, and extraordinarily accurate. I imagine they re all digital but, particularly if you are working on some industrial process involving filling and draining, you may find a solution there. They may not be so accurate on longer cycles as some of the air might dissolve in the water, but at least the sensor is dry, and not at the bottom of the tank.