Best answer of the lot - obviously a man who knows cars

In practice, only very small amount of water would enter through a 1 - 2" filler cap aperture, even if the rain was driven. The water will drop to the bottom of the tank (it's heavier) and usually remains below the intake, unless you run the car right down to the bottom of the tank (bad news for an injected cat car anyway, for other reasons). If it does come down the fuel pipe, it will bring a lot of junk with it, which will usually be caught by the filter, which you will see immediately by looking at it (if the filter is transparent, that is). The filter will not, however, stop the water - it will just get pumped into the cylinder head by the injectors (it's immiscible with petrol) as if it was fuel, and the engine will just die within a few strokes. At this point, the best thing to do is detach the fuel inlet pipe to the filter, switch on the pump to clear the tank (CAUTIOUSLY, with the help of a hygroscopic as Doug says) and then replace the filter and hoses. Refill, turn the engine a few times to pump it out, and you'll be OK.

Heck, I regularly change my bowl filter on the TR6 (which is mechanical injection) and there's always a few spoonfuls of water in there. Makes for interesting driving towards the bottom of the tank

PS. Now Doug, since you like V8 MGB's, wanna ask me about my experiences with a supercharged one with Nitrous and water injection? (tee hee)

PPS. Hint - "BANG"

One of the few remaining Mk1 owners... #00015