Still, sparkling or deluxe? Selfridges is set to open the UK's first H2O speciality bar, a teetotal cocktail joint that only sells different varieties of water.

The store is thought to be another establishment now seeking the advice of 'water-sommeliers' - people who are said to have trained their palates to taste the differences between different types of water, whether that's source, depth or mineral consistency. Though new to the UK, water-only bars have been opening in the US for a few years.

Molecule in New York City came under fire after its opening in 2012 for selling specially filtered tap water for $2.50 (£1.70). In 2013, a restaurant in Los Angeles hit the headlines when they unveiled a 45-page water menu created with water sommelier, Martin Reis.

In Belfast, the 5-star Merchant Hotel launched a similar menu last year including 13 exclusive varieties of bottled water - the most expensive being £26. Reis told the Sunday Times: "Water has a taste... [Different brands] can be salty, sweet, smooth, fruity, complex, metallic."

According to Reis, the differences in water brands are as striking as different kinds of wine: "Like wine, one can actually taste the region and depth from which the water comes."

Selfridges' water bar will open later this year in the accessories hall. The menu is still under wraps but some luxury water brands can go for over £100.

Still thirsty?