Probably depends on different airlines procedures. In our outfit if time is available the process is known as a "planned emergency" and we would try to carry out a some sort of Cabin crew briefing ...I guess a double engine failure at 30 West at Flight Level 380 might
just fall into that category.........
However if time is limited ( certainly the case here!) it becomes an "Unplanned Emergency"
All the Cabin Crew really needed to know is that there's going to be some form of hard landing
very soon and therefore they and the passengers need to be braced for impact....so all they'll get in that case is a "brace, brace" call.....IMHO in that case ( short time frame) you don't want to mention a landing on water - you want the crew and pax braced for impact,
not trying to don lifejackets at the moment of touchdown.