What is the difference between "water/drink enhancers" and cordial?

They wouldn't use the name "cordial" because it has a different meaning in the US. Over here, "cordial" is some sort of flavored alcohol, usually with a sort of connotation of something that rich people drink after dinner or as something refreshing that some rich people on a southern plantation might drink. (so it's not only alcoholic, it's classist/elitist, too)

They wouldn't use the term "squash", either, as to most Americans, that's a vegetable or maybe a sport that rich people play.

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I'm not aware of any specific food labeling requirement, but the term "water enhancer" is fairly well known to Americans who go camping, drink well water, or disaster preppers. It's used as catch-all term for anything to be added to water to improve its flavor.

So it would include powdered drink mixes such as Tang and Kool-Aid, which is why I would assume they specified that it was a "liquid water enhancer" to distinguish themselves from those other things.

But in the past few years, there have been a few companies selling tiny little squirt bottles of flavorings for bottled water. (the first one that I remember seeing was Mio) They're not like liquid drink mix concentrates like what you're describing, as they're typically just a few drops to flavor a bottle (500mL) of water instead of something that's diluted around 1:5, like you would for a flavored heavy syrup.

So basically, not only does 'cordial' not mean the same thing in the US as it does in Australia, but what you're dealing with isn't exactly the same as a 'cordial' from Australia, either.

Apart from in America, "cordial" is often a term for something based on sugar and fruit. It's more commonly called "squash" in the UK (but one old brand is Rose's lime cordial); in other languages the name often translats to "syrup". Many are brightly coloured, whether artificially or using various plant extracts in addition to the juice that contributes to the flavour. This has changed a bit in recent years as sugar-free varieties have become more common, and less awful.

In the meantime there's been a growth in clear flavoured water ready to drink in bottles.

The various concentrated flavourings for water that are now available aim at a slightly different market to cordial/squash/similar products, closer to the target for flavoured water but without the same plastic waste concerns. The typically sell on the hydrating benefits of the water, and any healthy claims they can imply about plant ingredients. There are even tea bags meant for adding to your (cold) water bottle. While the brands might be owned by the same multinationals, these new products tend to use the names of mineral water or tea companies.

Overall, though often very similar as you've identified, these products aim to be more upmarket and aimed at health-conscious adults (at least here in the UK, the equivalent to Australian cordial is seen as a bit of a children's drink, though widely consumed by adults).