That would be a very nice phrase to have indeed! Unfortunately, there are not any "common phrase" for wishing people a "nice shower" in English. It is just not something people say. First of all, the use of such a phrase is limited. Unlike cultures where communal baths are a sacred tradition, Americans tend to be prudes and would generally not be caught dead bathing with mere colleagues and acquaintances. Generally, only family members have the opportunity to see each other go into a shower or the bath. And generally, family members don't wish each other a "nice shower." The closest thing I can think of is perhaps at a gym (fitness club), where acquaintances *MIGHT* say "enjoy your soak" or "have a good soak" to someone going into a hot tub. After the soak, you could ask "did you have a good soak?" On the other hand, I cannot even imagine wishing a fellow male gym member to "enjoy your shower" or "have a nice shower" (except perhaps as a joke) or "have a nice bath." I would certainly not say "Hope you had a good shower" after the fact, either...

Alex, Someone might ask after a person has left the bath, "Did you enjoy your bath?" Which would be perfectly acceptable, especially if in a close friend or family members home. However, if someone is heading into the bath, you could say... "Enjoy your bath." is perfectly acceptable. It really just depends on the closeness of the relationship with the other person. Even just saying..."Enjoy" is fine too; as I do this with my friends and relatives quite often.

No. What's more, such a communication at best, is trite and superficial, equivalent to telling a person to enjoy brushing their teeth or using the toilet. If I was in a person's house, and they said anything at all about my private activities in the bathroom, I would think it wise to avoid further contact and remove myself from their house as soon as possible.