If the lab is going to check for trace benzene in the water, ideally you would have some pure material for reference purposes.

Put that in perspective against industrial quantities where a hardhat operator opens the hatch on a very full compartment of a chemical tanker, looking at their mirror image reflecting up from the surface of a few hundred tonnes of cargo a few feet below.

Which is then carefully sampled and delivered to a lab where they check for trace water in the benzene.