Summer project: Pop-in-pot cooler

In 2000, Nigerian teacher Mohammed Bah Abba won the Rolex award for inventing the Pop-in-pot evaporation cooler. It so simple, put one terracotta pot inside another, and fill the gap with wet sand. On dry days, the water in the sand evaporates through the porous clay of the outer pot, cooling the contents much the same way that sweat cools the body. This simple device, which uses no electricity, keeps vegetables fresh for up to nine times longer than usual in the harsh, dry Nigerian climate.

So, I was thinking I'd like to bring a little Nigerian entrepreneurship into the backyard this summer, and build my own pot-in-pot cooler, to keep the drinks cool at barbies. It's a hell of a lot more energy efficient than starting up the mini-fridge! And a great way to subtly promote sustainable living among friends and family. (There are instructions on how to build one at instructables.com - one of my favourite websites.)

My only concern is that Sydney summer's won't be dry enough for the pot-in-pot to work. If not, perhaps the traditional Australian version, the Coolgardie Safe, which works in a similar way, would be a better option. Anyone got any pointers?