In the first time, connect the first flow meter in the inlet of the vessel (inside the vessel make sure you have the glycol, after the gas passing thru the vessel, connect another flow meter and them it possible for you to know the variation of volume ( inlet - Outlet). The glycol absorb the water contain in the wet gas, after you obtain only dry gas.
Depends on the service. Free water in natural gas is found in the upstream environment and normally extracted at process. (separator or scrubber). Various on-line devices can measure water in a range of gas void fractions, the solution depends on the cost and relevence of the problem.