Rik,
Gasoline going through a carburetor turns to vapor. Water doesn't vaporize  
real well. I was with a friend on a pontoon boat when his engine sucked the  
water from the bottom of his tank while going full throttle. The end result was  
the total destruction of the top end of the motor. It blew the head gasket, 
bent  the rods and crank, cracked the pistons and totally ruined the engine.
 
Rummy