The availability of clean water is one of the most significant challenges facing the world today. Polymer membrane technologies for water purification are one of the most promising solutions to this problem. We are developing quantitative measurement methods for determining the structure and dynamics of polymer membranes used in water purification, as well as how these properties change over time or after various processing treatments. To facilitate these measurements, we are utilizing a molecular layer-by-layer approach to fabricating model polyamide membrane materials with defined internal structure and chemistry. To probe how membrane structure and dynamics correlate to transport properties, we are applying and refining approaches based on x ray and neutron reflectivity, dielectric spectroscopy, advanced chemical spectroscopy, and scanning probe microscopy. The structure-property-performance relationships obtained from these measurements will enable industry to identify the fundamental mechanisms underlying water transport and fouling, allowing targeted development of membrane materials with higher flux and lower energy consumption.