Nice glass of fizz?

Given that my health problem is controlled with isotonic drinks I was sick of having to buy bottles of powerade and cart them back up the hill and up my stairs every week. The Boy, being his usual helpful self, found some tablets on the internet that get dropped in to water and provide all the essential salts and stuff that the energy drinks provide. Better still, they only take up about an inch in the cupboard rather than a whole cupboard themselves.