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Shuttling water around, though, depends on having a bucket big enough and high enough to put enough water into to matter. A big ol’ bucket of rust might be easier to site if you don’t have a dam or a hillside reservoir handy.

I think this was just poor wording in the article. My local power company (Dominion Energy VA) recently started a huge iron-air battery project because the technology supports 100 hours of active discharge [0]. I'm sure there's some background discharge, but it takes a lot longer than 100 hours for iron to naturally rust through.

[0]: https://www.pbs.org/wgbh/nova/article/iron-air-battery-renew...

Pumping water up requires massives amounts of water, rarely available for regular homes