Have you tried making stalls for each shower / toilet / bathtub? If you put up walls to separate them and use the stall doors, it should be alright for a communal bath?

Perhaps Ideology could fix it?

Especially if you make it gender-specific, so men can shower with other men (and women with women) without negative effects, unless they have the prude trait in which case they always have the negative effect. I agree this should be added.