From an ops manual
Land Immediately The urgency of the landing is paramount to assure the survival of the occupants. Land in the ocean if these emergencies occur over water and other alternatives are not available.
Land as soon as possible Land without delay at the nearest suitable area (eg open field) at which a safe approach and landing is reasonably assured. These emergencies would not normally necessitate a water landing.
Land as soon as practical The duration of the flight and landing site are at the discretion of the pilot ie normally would necessitate a return to home base if over water.
Note - this is for a offshore operation