Risk management
Over water flights do have a risk but this can be reduced and managed by some simple precautions, there are two major issues :- staying alive in the water & being located by the rescue services.
As has been said above the water is cold with life expectancy of one hour in the summer and only 10 Min in the winter.
Life jackets must be worn at all times when over the water there is simply not enough room to put them on when the engine stops.
A liferaft is also a must as said above this must be attached to the aircraft when deployed I have a seat belt attachment on my liferaft so the seat belt is released to enable escape from the aircraft I attach the liferaft to the seatbelt, this has the advantage that no sharp items are needed to launch the liferaft and release from the aircraft is easy.
Once in the liferaft half the problems with the cold are over and the problem of being located are about to start.
When ever I fly across the water Box 2 is tuned to 121.5 if things go wrong it is then a quick call MADAY to the ATC unit that I am working and then off to 121.5 D&D have the kit to locate you quickly and can get the rescue assets launched. Next tune your GPS to the page that gives the nearest VOR and broadcast the radial and distance as you are decending with repeated reports as you are about to hit the water, For security reasons most airliners are now listening to 121.5 so a very accrate ditching location will be receved by a number of aircraft.
You should have an ELT once in the liferaft switch this on and wait when you hear the helicopter deploy your sea marker dye and flairs, flairs are good for attracting boats but sea markers are on limmited use for location by boats.
If you are flying and you hear a ditching in progress near you try to get to the location and see if you can locate the ditched aircraft (if they have broadcast a radial & distance then you can put this into the GPS as a used waypiont and go to the location, an aircraft overhead will help the peope in the water, just knowing that help is on its way is a great moral booster and you will help the reacue services quickly locate the people in the water. once the rescur helicopter is visual with the people in the water go away, your job is done and the helicopter crew don't need disturbance on the radio when winching the people out of the water.