What is the most precious commodity on earth? Financial markets give pretty clear answers. Gold currently trades at around $1,800 (£1,447) per troy ounce. A round, brilliant cut 1-carat diamond will set you back anywhere between $2,500-$18,000, depending on its quality.By contrast, a bottle of own-brand mineral water costs 1.9p per 100ml in a UK supermarket - which equates to 0.5909p per troy ounce. You can live a perfectly happy life without ever being given a diamond or owning gold bullion. But, as everyone knows, you can't even have a perfectly happy day without a drink of water....
