Well, no. You can breathe pure oxygen but you cannot breathe pure water vapor (H2O).
Pure water vapor at 100ºC ...
Aren't we breathing some water vapor now?
"you believe in water vapour which is oxygen. "
H2O is NOT O2, is it?
That's true. I'm breathing in both.
The science lesson for today is concluded. We're all breathing in oxygen and water vapor.
Has anyone learned anything? Almost certainly not. But I'll add some of my musings and you will learn.
What is the danger of suffocation from oxygen deprivation in a closed room?
First, how much air do we inhale and exhale per minute? Answer: About 1 cubic foot.
Next, how much oxygen do we remove from that volume? Answer: About 1% of the 9%, leaving 8%.
So a room 12 x 10 and 8 feet high will permit one occupant 120 x 8 x 9 minutes of oxygen or 8640 minutes which equals 144 hours before exhausting all the oxygen. Sleep well. Before ever approaching this limit, the carbon dioxide concentration would undoubtedly cause adults to hyperventilate and wake up, opening windows or/and doors.
One evening, I was sleeping in my Volkswagen camper in the snowy mountains and I had the bright idea to heat it with a catalytic heater inside the camper with my wife and me. Window slightly cracked. I woke up around 1 am with a splitting headache from either carbon dioxide or oxygen shortage and turned off the heater before we all died. Don't you do this. Charcoal briquettes are far worse. They produce carbon monoxide, very deadly.
In his book, Counting the Eons, Isaac Asimov, an ignorant atheist (but I repeat myself) said "If you breathe underwater through rubber hose that is long enough, all the air will not be exhausted and you will suffocate." How stupid of Isaac, for two reasons.
1. Straightening a snorkel puts your chest down deep enough that the water pressure prevents you from taking a single breath.
2. BUT EVEN IF YOU COULD inspire at 50 feet deep, say, you could exhale through your nose, and inhale through your mouth. I've done it by cracking the valve on a scuba tank, testing survival technique in case of total regulator failure.
"If you throw an object up in the air, it goes on forever." - Isaac Asimov, Ibid
I wrote to his publisher pointing out his silly mistakes. What a doof. He was afraid to fly in commercial jets, and abandoned God when his prayer to pass a chemistry exam was not "answered."