Until recent decades, the most common material for rainwater tanks seen in the Australian outback were corrugated steel tanks. These tanks were often galvanised, which is a process where a protective zinc alloy is applied to iron in order to provide an electrochemical protection against rust and corrosion.
Galvanised steel is found in many products including nails, bikes, wheel barrows and of course, your traditional corrugated iron rainwater tanks that often litter rural properties, more often than not in a rather poor state due to years of being exposed to the weather.
Numerous factors affect the life of a galvanised coating including environmental conditions, the usage of a product (e.g., roofing, sheds and water tanks), contact with chemicals and dissimilar metals, method of galvanised coating and the coating thickness. A more thickly zinc coated steel tank of 450g/m2 would obviously outlast a thinner coating of 150g/m2.
Galvanised steel tanks will come with an inner poly lining. This provides additional protection to the steel tank from the rainwater stored within causing rust and corrosion. It also helps to prevent leaks at welded joints, which can be a weak point in steel tanks and a cause for water leaks. The inner poly lining in galvanised steel tanks also stops zinc leaching into your rainwater. Zinc gives your water an unpleasant metallic taste, but is otherwise safe to drink.