Intermittent fault code

[monty quick]

'System Fault Code 128 - Water Sensor' has come up 3 times in the last few weeks. I can clear it and it has returned after many miles on one occasion and just after starting on another occasion. I had someone look at the logs and they say it has not been logged.
Any ideas of what the code refers to and if I should be worried about it?
Thanks in advance.

[Cerberus90]

Don't think it's anything to worry about, my Dads T350 occasionally pops this one up, usually when starting but sometimes at other points, seen a few other cars do it too.