I would have used skim milk GHM as that's all I have in the house. I think the carbonated water helps with the puffiness of the yorky although it is not something I used pre-TMX. I wouldn't add plain water, would probably use milk as a replacement to make up the quantity of liquid. I'm sure they will work but if you possibly can try and stick with Hestonfan's recipe as close as possible you will be delighted with the outcome.