The exercise gym I go to has a single room with about 8 or so shower heads with no dividers of any kind between them, just 8 shower heads in a room with a drain, and no door to the room, either (open on half of one side). It's like that for the women, too, and I'm pretty sure it's not the only gym like that.
It doesn't matter how many women might find themselves taking a public shower like at an exercise gym, because the only women who would possibly be affected one way or another by who turns up in a public shower are the women in a public shower. Perhaps there was some context to your comment up thread that I missed?
Assuredly less than 100% of all women, but the issue only concerns the women who wind up in a public shower, so it's 100% of them (who would be potentially impacted).