Jody's site says if you add more than 8 oz, you will need add'l preservative; WSP says only that you can add water if it's too thick, with no specific amounts given. I emailed Jody and asked for clarification, but haven't heard back from her yet. I have ordered a sample of the NG MultiBase; if this one is good, I may just go with it. They give clear, concise guidelines of how much water to add, and also that the preservative in it is Germaben II, just in case you did go over and needed to add more. I just feel safer with a supplier who is more forthcoming with their product information; if it were a candle, it would be different, but this could be a health hazard and I don't want to take chances.