Why are you using an appliance attached to a mains outlet in the shower?
EDIT: Misinterpreted your post but unless you are showering outside atop a defoliated hill you would be at no risk whatsoever.
this might be cr@p (it's mythbusters- they were testing to see which things were safe to do in electrical storms), but if your house gets hit, because you're standing in water, it'll get you too. also, the shower is attached to the mains etc. too, as far as i'm aware (talking about power showers here).
don't get me wrong, i'm aware it's incredibly unlikely, but people do get struck by lightning. A teenager died last week after getting struck in a park in birmingham (if i remember correctly)... :(