Just two or three years ago sales looked set to continue a decade of spectacular growth driven by increasing interest in health, an expanding economy and clever promotion.
Now the first evidence of falling sales has marked the turn. What happened?
The truth is that for most people, most of the time, tap is the nation's choice and always has been. It was always questionable to compare it with a consumer product-child of its time that danced like a beachball on a fountain of lifestyle froth and celebrity.
Now the light has dawned and reveals, not shiny high-status people or limpid mountain streams, but a networked public service that benefits everyone. In place of froth, we have quality, reliability and value for money; in place of 'lifestyle' advertising, we have concern for the environment.
And just as generations ago the public water service brought a permanent improvement in the national health, we now see it can play a big part in helping tackle climate change.
Of course it makes sense to provide mains water rather than bottled in schools, hospitals, factories, offices and restaurants. Of course transporting water half way round the world and lugging heavy litres from the supermarket each week makes very little sense.
Accepting all this, is it really right to demonise bottled water?
High quality water is good for you whatever its source. Bottled water has a vital role if a mains supply is interrupted. And aren't bottled brands better partners for on-the-move lifestyles than sweet fizzy drinks?
For most people, most of the time, UK tap water is the right choice for quality, health and the environment. But let's not get carried way.