No-electricity automatic waterer

I was recently fiddling around with self-watering planters.  Yeah, you can't grow as much as in the ground, but they're great for decks, driveways, and other places where that's not possible.  Plus, we plan on adding a few inside the house for winter growing.

Anyway, I thought I'd share my latest innovation in that arena.  While the above are somewhat self-watering, which is nice, water still needs to be added from time to time.
My idea is to make the task of watering completely automatic, rain-barrel compatible, grid water fail-safe, AND without needing any electricity!

This improvement works with any watering arrangement that uses a fixed level of water, including:
Either the 5-gallon poly bucket variety ("Alaska" buckets)

Or more of a raised garden bed (SIP sub-irrigated planters)

Or it should also do great with animal watering systems.

The secret to making this happen is a poly bucket with a pair of cheap float valves ($3 apice on amazon)

To set up, the height of this bucket is raised or lowered so that the "max" line is the same water level as the planter's and a funny-pipe hose run from this to the bottom of it.  The higher float is run to the rain barrel, and the lower is attached to a garden hose.

Here's how it works:
1) When the level drops below the "max" line, the first float turns on and water from my (higher elevation) rain barrel refills the bucket (and therefore the planter) up to the correct level.

2) If water ever drops below the "min" line, then presumably the rain barrel is now empty, so the second valve turns on to at least maintains the minimum acceptable level using regular tap water.

Well, I hope this idea is something useful that you guys can add to your own projects.