I had the same problem a couple of months back, plenty of tread on the spare but the wrong direction. I wouldn't recommend driving in the wet with it the wrong way, best thing is to get the punctured one repaired/changed asap.
I waited a day for the roads to become dry again before driving on my spare. If you must drive in the wet just take it nice a slow, try not to drive on the motorway above 60.
Lee.