Well after searching like a mad woman, I managed to find a flavoured water that doesnt have citric acid:
Perfectly Clear Still - Strawberry and Kiwi:
Ingredients: Spring water, Malic Acid, Aspartame (OK not so great) and flavourings.
Carbohydrates: Nil
I've been out shopping so am 1 litre behind where I would normally be at this time of day so I'm about to catch up with a few glasses of this.