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Water and ethanol vapor adsorption phenomena are investigated systematically on a series of MFI-type zeolites: silicalite-1 samples synthesized via both alkaline (OH^–) and fluoride (F^–) routes, and ZSM-5 samples with different Si/Al ratios as well as different charge-balancing cations. Full isotherms (0.05–0.95 activity) over the range 25–55 °C are presented, and the lowest total water uptake ever reported in the literature is shown for silicalite-1 made via a fluoride-mediated route wherein internal silanol defects are significantly reduced. At a water activity level of 0.95 (35 °C), the total water uptake by silicalite-1 (F^–) was found to be 0.263 mmol/g, which was only 12.6%, 9.8%, and 3.3% of the capacity for silicalite-1 (OH^–), H-ZSM-5 (Si/Al:140), and H-ZSM-5 (Si/Al:15), respectively, under the same conditions. While water adsorption shows distinct isotherms for different MFI-type zeolites due to the difference in the …