Koran mentions to have bath after sex with wife but no mention on wet dreams etc. But if you ponder on the Koranic instructions, you are unclean when you discharge
as you don't discharge just like that as there will be either due to wet dreams or masturbation and both are unclean. So follow Koran's instructions to have bath whether it is just discharge or after sex. Don't forget Allah in the Koran also mentions that in case of water unavailability one can Tyamam(Wudu with clean sand).
Allah Hafiz!
The Bible
If you think about it, you will have to agree that sex is a subject frequently addressed in the Scriptures, both Old Testament and New. Though the Bible handles this subject matter much differently than the secular world, it does have much to say on the subject. I can only think of one reason for matters pertaining to sex to be so frequently discussed in the Bible—sexuality must be very closely related to spirituality.