Use vinegar to revitalize showerheads
Father Time will eventually win, and he seems to have a personal grudge against showerheads. That’s the only explanation we can think of, at least, because calcification causes showerheads’ flow to be slowed down over time.
It is also possible to repair your showerhead if you’ve already reversed time but are still unable to turn it back. Simply fill a plastic bag halfway with vinegar and tie it around the showerhead. Let it soak overnight, and water pressure will visibly improve in the morning.