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One large gin and tonic is acceptable as a thirst quencher.[…]
For further, serious drinking I recommend gin and water- and ice and lemon. This combination is favoured by the understandably popular George Gale. My advice: make sure you don’t overdo the water. Gin and water is an all-round improvement on gin and tonic: cheaper, less fattening and less filling as well as being not sweet or gassy. Gin is a real and interesting drink, carefully prepared with those botanicals and all, and it deserves to be sampled with its flavour unimpaired…"
(Kingsley Amis, Everyday Drinking, p.104 f.)
I find this completely acceptable also with mineral water, too. We in Austria have some excellent mineral waters by the way...and they also have a certain cachet since they are not widely known.