There will be some water vapor produced by the process but if the amount is larger than expected this can be caused by "fully wet-out" membranes. Normally the PP hollow fibers are wet on the shell side and dry on the lumen side, and the pores are dry. The pores can wet-out if cleaned with a surfactant (not recommended).  They can also wet-out if shell and lumen are both full of water.  We recommend that the Liqui-Cel be dried out over a 24-hour period.  Please find the procedure “3M-Liqui-Cel Cleaning Guidelines” in the downloads section of our website.  This procedure mostly is draining the module, running the sweep gas (or filtered air) at the gas inlet, and pulling a vacuum to pull all moisture out of both sides and out of all the pores.  We also recommend that a small N2 sweep gas is used.