An egg has millions of holes in its shell. It absorbs the odor and substance around itself very easily. This creates a bad taste if it’s kept in the fridge with other food ingredients. This shelf provides a place for eggs outside of the fridge. Also the freshness of eggs can be tested in the water. The fresher they are, the further they sink.
Everyone in North America stores their eggs in the fridge, but few people in Europe do, they can last for days on a shelf or in a pantry. In European supermarkets, the eggs are not refrigerated. Integrating the water into the egg storage shelf is really clever; according to about.com, if an egg:
Sinks to the bottom and stays there, it is about three to six days old.
Sinks, but floats at an angle, it’s more than a week old.
Sinks, but then stands on end, it’s about two weeks old.
Floats, it’s too old and should be discarded