In my post on Saturday, one of the things that was cited as an example of bad worldbuilding was the lack of bathrooms:
"You give me in excruciating detail the pyramids, palaces and every other prominent place within a thirty-mile radius, but there are no bathrooms or toilets anywhere."
Well, I do have something to say about that. The reason why bathrooms or toilets are not present is that no one feels they are relevant. And guess what? Most of the time, they are not. It would be easy for an author to consider them unpleasant and skip over them for that reason. There are people out there who really want to create "gritty" worlds and will make sure to include toilet details for that reason, but not everyone falls into this group.
When you're writing a story, you can count on your reader to use inductive reasoning rather than deductive reasoning. Why is this important? Because with inductive reasoning, a lack of evidence for something can in fact imply that that thing doesn't occur, or doesn't exist.
Extrapolating from this, you can imagine that we don't want anyone to conclude erroneously that there are no toilets in this world. How do we fix this without spending undue time on it?
The easiest thing to do is to use small instances of cleanliness issues. I'm thinking of Nya in Janice Hardy's The Healing Wars series, who at a certain point dips a sock in the lake to clean her face. Immediate implication: she has no bathroom. Janice also mentions bathrooms in the case of Nya's friend Aylin, who lets Nya use a communal bathroom down the hall where she lives. The result is that the mention of cleanliness and the bathroom will imply attendant issues of toilets without the author actually having to go there. Of course, there will be places in your story where the lack of a toilet may actually be relevant (as in a long ride, etc.) and an oblique reference to stopping behind a tree might not go amiss.
In my current novel in progress, For Love, For Power, an unusual amount of time is spent in bathrooms. No, it's not particularly gritty or dirty! For this story, the bathroom focus is on bathing, and it serves a specific purpose: it is often an ideal setting for me to explore concepts of privacy, safety, and intimacy that differ greatly between social groups, and are highly relevant to the story. In fact, my characters head to the bathroom in the two opening chapters.
In chapter 1 my main protagonist, Tagret, gets caught in a mob panic when a concert crowd witnesses a death and concludes that the virus Kinders fever might be "loose" in the room. It's perfectly reasonable for him to hurry home and get straight into the bath... and having his brother pick the lock on his bathroom door and interrupt him is the perfect introduction to the nature of their relationship.
In chapter 2 my second protagonist, Aloran, is about to interview for a job as manservant to Tagret's mother. The nature of the position of manservant is highly relevant to the kind of delicate issues he'll be facing with the family, and to many of his personal struggles in the book, since the Lady won't have an easy time accepting his service - so during the chapter I try to show the range of his duties. The business end of it gets covered in the job interview, where he's tested for his bodyguarding skills and his ability to judge social situations. However, he's also expected to wash his mistress without becoming emotionally involved, and that's the sort of thing that benefits from a bit of show-don't-tell. So before he heads off for his interview I have a young classmate of his ask him to help with practice for the bathing exam. The students at the Academy are required to demonstrate that they can bathe the person they find most attractive without showing signs of emotional involvement - so off they go to the showers where Aloran coaches his friend through the process that he has mastered, but his friend is still struggling with.
The juxtaposition of these two situations, each of which is only a tiny section of the chapter in question, provides a useful and highly relevant contrast between the characters and the social groups they belong to. Each one also sets up expectations for where the different characters will feel discomfort in the story as it continues.
So in your story, particularly if you're writing a novel which will cover a lot of ground (because story-relevance has to be a lot stricter in short stories!), I urge you at least to consider the question of bathrooms. To mention them often might be gratuitous, but to omit them entirely can appear ridiculous. And as you can see, in some cases they can be a great ally in helping you explore questions of intimacy!
It's something to think about.