Although I am very sure that you already tried the well-known Karl Fischer titration for that, this is still the most often used method in industry and research to determine the water content.

I think this paper is very close to your research topic, since they also determined the water content during biomass pyrolysis:

http://pubs.acs.org/doi/pdf/10.1021/ie070684k

try to use Dean-stark setup, where you will evaporate the water and condense it while the oil and other material will go back to the vessel .