It used to be about 12%, but after the Tacca incident they figured that the processing energy necessary inside the engine was more related to temperature and state e.g. is the water partially contained as a frozen state like hail.
Rain is pretty insignificant in the bypass section and the amount that gets into the compressor is affected by the fan spinner shape so 12% water entering the inlet does not translate to as much as 12% going into the compressor. However like I stated earlier if you put the water into the compressor as hail it's a lot more potent.
For rough ballpark numbers it would take in excess of 30% water alone in the compressor to cause the engine to spool down at flight idle. Of course if you manage to operate the engine at something lower than placarded flight idle these numbers are meaningless.
To put it in real world standards the CFM56 engine can sustained better than one in 100 million storms