Honestly, I would use my SodaStream machine if the cartridges were not so prohibitively expensive in the UK - £15 per refilled cartridge via Argos (being one one the few remaining places where cartridges can even be had).

Feels like Pepsi could revolutionize the carbonated water market in the UK/US by having machines installed in supermarkets to allow filtered bottled water on demand at better prices. Also, feel good and environment factor would be top given no CO2 emissions from trucking tap water around after fizzing it up!