I Found A Long Thin White Worm In My Cats Water, What Would This Be And Where Would It Have Come From?

I found something in my outdoor water bowl that looked like a thick thread. I took it out and found that it was alive. It was probably about 3 to 4 inches long, maybe more and about the thickness of a straight pin. I am sure this is some sort of worm, but cannot figure out how it got there and what it is. Should I be alarmed?