What happens to a water molecule when we ingest it into our body?

Question

Does it remain a water molecule until it is expelled from the body in urine or sweat or whatever, or is it broken down into H and O and these elements are used by our bodies?

Answer 1

You should understand that water has a tendancy to naturally break into parts. Not completely, but into an H and an OH. This is why the pH of pure water is about 7 - water by itself is a weak acid.

Because of this, if you were following a water molecule even in a glass of water, it wouldn't be too long before the three orginal atoms were in three different molecules. Nor is it any different in your body. Still, most of the molecules in your body are water, so there's a pretty good chance that those three atoms that went in as one water molecule would still come out as water, albeit in different molecules.

Now, your body uses hydrogen ions for all kinds of things. They're involved in energy production, nerve signals, and of course in assembling some of the stuff in your body. So there is some chance some of those atoms could be waylaid for a long time. But again it's not like your body specifically breaks the water molecules down. It doesn't have to... there's enough parts lying around that one is always available.