well, in all of my 72 years i've never heard the phrase "water closet".
then again i thought hummm well maybe she lives in some other country like Africa and water is in short supply there so they have a special closet set aside to store their water. now if she had said "OUTHOUSE", I surely would have known what that was as we had an outhouse when i was a kid growing up. which proves we're never too old to learn something new.