I don't. I adjust water based on if I want gel or not, if I'm swirling, if it's a castile and things like that. I don't account at all for the liquid amount of the fragrance. It's generally not a lot, esp for EO's which most people use at 0.5 oz ppo or so and FO's at 0.5-1 oz ppo (in general. People use quite a variety of ratios, of course), compared to the amount of water rec'd at "full water". It will be interesting to hear if other people do or don't.