I call it the “loo”–I have been for as long as I can remember, and it’s just habit now. I’m not British, I just like the way it sounds.
I usually say restroom although when I’m on the boat we call it a head.
Yep. That’s how I voted.
This is my answer too, so I can’t answer the poll. 
I take it that by “bathroom” you do not mean the room where you go to have a bath, but the room where you go to piss and shit.
While living in America, I trained myself to say “bathroom”, despite the inaccuracy. Now I am back in my native England I am retraining myself to say “toilet”. If I said “bathroom” I would be misunderstood. In certain company (male friends that I have known since I was at school), I might say “bog”.
In the US this is one and the same, anyhow. Even if it was just a hole in a closet, it’d probably still be referred to as a “bathroom”.
Though I’d be tempted to call it the “shithole”.
My bathroom consists of a bath, shower, two sinks and a HWS. No toilet. 
If I was traveling and needed a toilet, I would ask “Where are the nearest public toilets?”.
If I’m at a friend’s house, I would ask, “Where’s ya dunny?”
If I am visiting an acquaintance, or for whatever reason a guest in a household that I am unfamiliar with, I would ask, “May I use your bathroom?” (even though it is unlikely that the toilet is IN the bathroom). It is understood that bathroom means toilet, but the term is only used in the most genteel of circumstances.
Inhouse
HWS?
Hot water service. Big tank thing, in its own little cupboard, powered by gas.
Forgot to add and missed the edit window…I’m Australian.
Bathroom at a home, restroom otherwise.
Terlet.
Shit house.
The Throne Room.
Depends. At home I have a “bathroom” on the second floor, plus a small “lavatory” downstairs. Out in public, I might ask where the “restroom” is.
If I’m talking about a room with a bath or shower in it, “bathroom.”
It it’s a room with a toilet in it, “toilet.”
At home: bathroom
At a restaurant: ladies room or mens room
Anywhere else in the US (client’s, attorney’s, or accountant’s office): lavatory
Other countries: whatever the local term is for lavatory
I’m British so I call the bathroom the bathroom. I call the place for spending a penny the loo. Very USocentric poll.
“WC” seems to be quite common for signage on the continent of Europe, including the UK.
I always say bathroom. I have a buddy who always uses the term “shitter”. Weird.