Took a walk down to the fields on either side of the railway track to see if anything was stirring yet. There are prints - but are they rat? And burrows - ditto. Plenty of feeding signs, too, but that could be field vole (I saw a field vole run past as I was peering down a bank).
Time will tell. Weather/temperature permitting, I'd expect to see water vole latrines appearing within the next couple of months. They are the best indicator of w-v presence, bar an actual sighting.