I have tried this experiment to its limits with an old Mk1 33 I wanted to scrap last year.
I took it in muddy fields , chasing after big paddles in order to make the mud and water splash as high as possible, and get the most mud on the roof of the car
The only time the engine stopped was when I was driving with high speed into a mud puddle as big as a small lake !!!
Luckily , I was going in such speed , I was able to go cross the other side. Otherwise it would have been messy
The engine was completely wet. The sparks are the first to get wet and cause the problem, the dizzy is way up but can still get a lot of water in it from these actions.
I fixed those two problems with lots of silicone stuffed around the spark cables and around the dizzy, so I kept going at it like a 3 year old child
Finally, the water got through the air filter, and ended up in the oil of the engine, causing the big end bearings to wear and finaly blew the engine up !
It was fun !!!
This was a very extreme example though... I think I posted a video on youtube last time... cant remember