Water depth detection for a road vehicle

A road vehicle 1 comprising a primary sensor set 10, 11 is described. The primary sensor set 10, 11 is arranged to detect water depth at a first set of locations within an environment external to the vehicle 1. The first set of locations are spaced relative to the vehicle so that the extent of the vehicle's submergence at the first set of locations can be predicted before the vehicle travels to at least one of the first set of locations.