what it's made of is directly related to whether it played a part. if it was a wooden barrel sitting in a tropical island it isn't going to last very long, nor is an iron barrel. 47 years is a long time for anything to be exposed to humidity and salt air.
I thought the same thing until I read up on galvanized. Highlights below:
The process was first invented by a French chemist in 1742, and first used by Stanilaus Tranquille Modeste Sovel, another French chemist in 1836. By 1850 in Britain the galvanizing industry was using 10,000 tonnes or zinc per year for the protection of steel. For the past 150 years the process of galvanizing has been sucessful as a method of corrosion control.
The performance varies in different environments. In warm and dry environments the stability of zinc is remarkable. There is no reaction between the galvanized coating and the air so the protection continues.
In the presence of moisture in the atmosphere, the zinc stays stable indefinatley.
In rural areas, the life span of galvanized coatings may be reduced as the effects of aerial spraying and fertilisers.
By the sea coast the corrosion rate is increased because of the presence of soluble chlorides. Still, the protection of the galvanized coating is alot better than other protective systems, and can be further increased by a using a duplex galvanizing-plus-paint system.
Galvanized steel is chosen because it is very durable. The service life for galvanized steel is over 70 years without maintenance. Galvanized coating can last 70-150 years without maintenance in most urban and rural atmospheres.
Whether or not there would be water present and whether or not it would be drinkable is another matter entirely.
LTM,
Don