I'm in charge of the gardens in the yard, and the wife grows her
houseplants, windowboxes and plants on the balcony. I've got rain barrels
set up that provide more than I need for my square foot gardens.

I'm trying to envision some kind of on demand pump system that would let
her fill her watering cans from a rain barrel that is located one story
below her balcony. She opens the faucet on the balcony, the pump kicks in
and fills the can. She turns off the faucet, the pump shuts off.

I guess that an on/off switch on the balcony controlling a sump pump in
the barrel would work, but I'm looking for something more elegant.
(Just a classic brass faucet in her "decor" area of the house.)

Any thoughts?

Joe