Scottish Elises

I've been getting water into my spark plugs. Any suggestions on how to avoid? I use a cover over the grills when parked up but the rain was so heavy driving home tonight that it started spluttering down to 3 cylinders.

Oh and it was a new alternator that was required, not just a fan belt

Sorry, just noticed the existing tread on the same topic. Looks like I'm not the only one with the problem.