auto fill device?

Does any one have a way to keep their water feature full with out doing it
by hand? I was thinking there must be something out there that can be tied
into a water supply that would open and shut off when a the water level
reaches a set level.
I would like to put something like that on my front yard water feature that
is just a whisky barrel that pumps water up through a hand pump. But need
to fill often here in Colorado unless I can find and install a device like I
am asking for help on.
You can see the set up at
http://www.ofoto.com/I.jsp?c=65zgxlu...&x=0&y=-n2twfr
Thank you for you help I know there must be some way to do this.
--
Greg &/or Kellie Meyer