A passive sampler specifically designed to measure perfluoroalkyl and polyfluoroalkyl substances (PFAS) in water was tested in four study areas (Ellsworth and Peterson Air Force bases, CO and SD; the Ohio River, OH, WV, KY, IN; and the Santa Ana River, CA). Locations included both groundwater and surface water locations. Over the 2‐year study, 96 passive samplers were deployed at 33 sample locations and were compared with co‐collected grab samples, all of which were measured for 19 PFAS analytes by HPLC–MS/MS. Correlations were observed (typically within 2× difference) between aqueous PFAS concentrations measured by passive versus discrete grab samples across over 5 orders of magnitude in concentration (0.5 to 150,000 ng/L). Overall relative percent difference between grab and passive results displayed a median of 18% (interquartile range of −19 to 73%). Detection limits were around 1 ng/L for a 2‐week sampling time with sampling rates ranging from 12 to 70 mL/day in flowing systems. Duplicate samplers were deployed in all study areas which indicated a 14 to 42% (median 24%) relative standard deviation in the precision of passive sampling. Larger variances were seen with sites with higher and potentially more variable water flows. A sub‐set of duplicate samplers were measured by a commercial laboratory which returned equivalent data to research laboratory measurements (43 [±26 SD]% relative percent difference). Standardized protocols and calculation methods were developed to facilitate expanded testing and future broader use of passive sampling for PFAS by site investigators.