What Is This?

I have found a tiny beetle-type thing in my water.

I have no idea how it got there. For reasons of my own, I boiled some cooler water the other night. I let it cool on the stove-top overnight and poured it into my metal cup the next day so that I could take my ranitidine. When I came back from school several hours later, I noticed something strange swimming around the bottom of my cup as I drank. It looked like this, but extraordinarily tiny -->.

I am at a loss to explain how it got there, or even what it is. I've seen them swimming around in pond water sometimes.

The problem is, there's no way it could have gotten into my cup:

1. The cup was dry from many weeks of disuse; I scrubbed it clean shortly before I used it, then dried it again.
2. The water was already drinkable, and boiled
3. The tap water is treated; I've certainly never seen small beetles in it before
4. Even if there were something in the tap water, the cup was sitting many meters away from other bodies of water, like the sink and toilet
5. My apartment was locked and the windows closed. Nothing and no one got in or out.
6. I live on the 4th floor of an apartment that is nowhere near a pond

I guess it's possible that it got in the pot of boiled water overnight and I just didn't notice till later...but how? And from where? And what do I do with the little guy now?

This is one of those days that makes you go WTF.

You can see this too, right?
I'm not imagining this thing, right?

This is it up close.