How in the wood did that get there?

A weird thing happened yesterday, and I couldn’t help but pass it along as today’s new experience.
My house had two bathrooms, and one of those bathrooms has two washbasins. My wife uses the one on the left, and I use the one on the right. We’ve never had any problems with the water pressure in this house, but yesterday, as I began shaving, the pressure on my side dropped way off. The strong, steady stream that I was accustomed to had been replaced by a limp column of water.
I tried the water on my wife’s side, and it was normal. I finished shaving and during the ensuring shower, I pondered the problem. Bear in mind, that I’m not a plumber by any stretch of the imagination, so there was some bona fide pondering going on at this point.
Later, I screwed the cap off the facet. It was tough to turn barehanded, so I used a washcloth to get it started. When I finally got the cap off – lo and behold – I discovered the problem.
A small sliver of yellowish brown wood, no bigger than a long grain of rice, had gotten lodged in the hole in the center of the backside of the cap. The piece of wood was just big enough to disrupt the flow of water and cause the pressure to drop.
The question remains, though, how did this piece of wood get there in the first place? Again, I’m no expert, but I believe that the facet is the end of a closed pipe system that goes from the sink to the water pipe that leads into the house from outside. That pipe runs to my water meter, which connects to the Town of Excel’s water line that runs down our street. That pipe most likely runs to some sort of pumping station or to the nearest water tower. At some point, though, that piece of wood and likely others like it, had to have entered the system somewhere. In my mind’s eye, I picture it as being a piece of wood that somehow got into the water as it swirls around at the top of one of the town’s water tanks.
In the end, let me hear your thoughts on this. If you can clear up any misconceptions I have about how the water system works, I’d also like to hear that as well.