Adam suggested (as a thought experiment only!) pouring a cup of water into a gas tank and then running the engine at high power to see what would happen. 

 

To extend the thought experiment, takeoff power in my Legacy burns a gallon of gasoline every two minutes, or 0.5 gallons per minute.  A cup of water, if it somehow stayed together, would flush through the engine in about eight seconds.  That's probably faster than I could react and switch fuel tanks, turn the boost pump on, and set up for best glide. 

 

Of course, if that happened just as I cleared the departure end of the runway, that could be a very long eight seconds.  The point is that at takeoff power, a slug of water in a well maintained fuel system would flush itself through the engine in seconds. 

 

I once owned a Caterpillar D2 bulldozer.  It had big capital letters cast into the Diesel fuel cap that is good advice for us all:  "BUY CLEAN FUEL.  KEEP FUEL CLEAN." 

 

Dennis

Legacy, 740 hours, no water detected in fuel sumps or gascolater so far.