If you didnt touch anything, you wouldnt have to attempt to restart the engine, as once the water has passed the fuel would go bang and off you go.
I admit, the maths is not perfect, but that is not the point i was trying to make.
My point is this devise is simply not needed. a much similar way to prevent water contamination is to remove the water before flight. as water is heavier than fuel it simply falls to the bottom of the tank, were it can be removed by conventional means. I have flown different types where water contamination is a real threat, i have seen several fuel testers full of water, a touch of airmanship is all that is needed to prevent any problems, not a big mod to the fuel and electrical system.