A grey day may have obscured the lofty views from Jason Atherton’s City Social bar up in Tower 42, but did nothing to cloud the clarity of its Reyka Glacial Martini, launched last night and being served at the bar til the end of June. This tipple should come with a “no hangover guarantee” – I could gratefully vouch for this godsend today. 

The Martini’s purity comes down to its logical combination of lava-rock filtered Reyka vodka swirled around an icecube of Icelandic Glacialâ„¢ spring water. But each and every aspect of the Reyka Glacial Martini’s preparation has purity in mind, from the hand-crafted, small-batch creation of Reyka Vodka’s natural filtration through ancient lava rocks, to its further distillation in a carter-head still, well before its ultimate pairing with the low-mineral mildly alkaline arctic spring water (sourced from Iceland’s Ölfus Spring, where else).

The Californian health craze for alkaline water is lapping at our shores it seems, hence Wholefoods is one of the natural spring water’s few UK stockists.

Reyka vodka, distilled by family-owned William Grant & Sons of Glenfiddich and Hendrick’s Gin fame, has already won them a Master award in the Smooth Category of the World Vodka Masters. For all its dryness, it gets the rounded-finish vote from us too.

Purity is often the payoff not so much of what you put in, but of what you don’t: Shaving shards off a solid block of ice made of the Icelandic Glacialâ„¢ natural spring water, City Social’s Bar Manager Tim Laferia spritzes a dose of Vermouth from what looks like a perfume phial in to the bottom of my chilled martini glass.“So much easier to deliver a precise amount this way,” he explains as he pours in a measure of Reyka vodka: Ã¢â‚¬Å“Technically Lillet Blanc is not a Vermouth, but when formulating this Martini, we chose it for its purity as it doesn’t contain Wormwood, the chief botanical of Absinthe”.

Well you learn something new every day. He tops the Martini with a parting spritz and a twist of pink grapefruit for the Reyka signature kick. One thing is clear: This cool Icelandic vodka is reason enough to zoom up to level 24 of Tower 42 this month.

The Reyka Glacial Martini, £12, is being served at City Social Bar throughout June 2016