Wish I could help, as Ive been looking too, last time on the diet there was a few, certainly tesco did it, cant remember flavour tho, there was also a tonic water in a couple of supermarkets that had no citric acid, but this time around whilst so far I have stuck to water only, I have yet to find any flavoured water with NO citric acid.
If anyone finds out I want to know, not for now, but later down the line. Im continuing to look so will let you know if I find one, but hopefully someone else will know!