No, @alex.at.biosphere, 15% water means 15% water.
The problem isn’t even the amount of water, though, because the max total water (at least in the azeotrope) is only about 6%.
The problem is the fact that essentially ANY water in the mixture causes the whole azeotrope (of which there is a continuum of ratios for all 3 components) to separate into 2 distinct layers… each of which have different percentages of all 3 compounds: upper layer has about 2/3rds heptane, very little water, and 1/3rd ethanol… the lower layer has up to 15% water, mostly ethanol, and about 5% heptane!
So if you have 6% water in the mixture (which it naturally pulls from air and plant matter), then that 6% water still causes ALL of the liquid to separate into 2 distinct layers which have the ratios mentioned above! Even if you only have 3% water, it still ALL separates into 2 distinct layers which have slightly different ethanol:heptane ratios, and only half the usual rations of water (i.e. top layer is 0.1% water instead of 0.2%, and bottom layer is 7.5% water instead of 15%)!
These layers obviously have very different extraction properties!
Yes, terpenes and other solutes may very well form azeotropes with one or more of each of the 3 solvent components, which would wreak all sorts of havoc on any calculations… but I can verify that the bilayer system still exists after solvent recovery!
@back2thefuture The point of denaturing is to make azeotropes that are very difficult to separate. Sure, one could probably make secondary azeotropes and fractionally distill the ethanol:heptane apart, but something is going to stay azeotroped with something else.