You can always use known values to you like measure the total weight, total volume and by knowing water density =1. Do you can always measure the water alone. Than when you have two fluids, the difference would be the missing volume due to the second fluid.
azeotrop means that a solvent and water forms low boiling point azeotrop, with excess of solvent water can be distilled and the lower phase can be weighed, it is that simple, just like in petroleum compounds testing