Diet Tonic Water on Refeed.

I'm drinking lots of diet tonic water, over 2 litres a day, and I'm not sure whether this is ok or not. I know you can have carbonated drinks etc.. but I'm drinking this instead of the sparkling water I was having on TFR.

I'm worried now that I shouldn't be drinking so much of it. Any ideas?

I just had a email back from LT and any diet tonic water is ok and there is no limit on how much you can drink.