Part of the everyday object series
I present to you: the everyday fay.
Its ancestor was born on the very first day.
It lives alone, but can work well in a team,
Only comes alive when its foot is engulfed in a stream.
Its head is what's most important to us,
The material therein is almost superfluous;
That which comes out, that is the prize.
Incorporeal, yet it made us modernize.
What is this everyday fay?