"Underwater egress training is invaluable for any pilot who flies regularly over water, regardless of the type of aircraft flown. 
As a matter of fact, passengers or non pilot crews who also fly regularly over water should consider underwater escape training".
Transport Canada Aviation Safety Letter, Issue 2/98

"Given that the physical impediments associated with escaping from a submerged seaplane are often not insurmountable, it is likely that many people do not escape because they are not adequately prepared to do so."
Damien Lawson, Transportation Safety  Board

A recent Transportation Safety Board((TSB) reported that of 63 pilots who died after a crash into water, 78% were located inside the aircraft (only 22% died during impact or drowned as a result of non-fatal incapacitation).

"Fatalities in seaplane accidents terminating in the water are frequently the result of post-impact drownings.  Most drownings occur inside the cabin of the aircraft.  However, those who survived often found difficulty in exiting the aircraft. 
Over two-thirds of the fatalities occurred when occupants who were not incapacitated during the impact drowned".
A Safety Study of Survivability in Seaplane Accidents Report Number SA9401  conducted by the Transportation Safety Board.

Most ditchings occur with little or no warning time; therefore, flight crew and passengers are caught by surprise.  Most fatalities due to drowning are caused by:

• disorientation
  
• unfamiliarity with escape hatches/handles
  
• non-availability of personal floatation devices
  
• head injury caused by improper use of helmet (unfastened or improperly adjusted)
  
• premature unstrapping prior to settling of aircraft.
  

The inverted underwater egress trainer (also known as the helicopter underwater egress trainer, HUET or dunker) is designed to train flight crew and passengers in "underwater egress"  in the event of an aircraft sinking or rolling inverted upon water entry.

This is a proven system, in both the military and civilian aviation industry, of saving lives by training personnel in egress procedures and instilling confidence for a successful underwater evacuation.