In the days when toilets were not as common, people in many cultures and civilisations had designated places to relieve themselves. But that cannot be said for the wizarding world. 

National Geographic

Pottermore posted a particularly nasty bit of trivia on Twitter saying that Hogwarts did not always have bathrooms. 

Before this, witches and wizards would just relieve themselves wherever they stood and then vanish the evidence with magic. 

Yeah. I know!

OMG Facts

Naturally, the Potterverse did not take this very well. 

Oh man, this seriously needs to stop. As funny as it is, it seems like they are just messing with us at this point!