We describe a low-field NMR relaxometry study of water and aviation turbine fuel (jet fuel) in contact with samples of fibrous media removed from an unused aviation fuel filter cartridge. This media was studied both in its as-received state and after modifying its wettability. The interaction of liquid droplets with fibers is the basis for fibrous coalescence widely used industrially to separate different types of liquid-liquid dispersion. Here, we are specifically concerned with interactions that potentially occur during the removal of entrained water from jet fuels, an application that is of particular importance on safety grounds, primarily to prevent ice formation in aircraft fuel tanks which could otherwise lead to fuel-line filter blockage and fuel starvation to the engines. Jet fuel is treated using various filtration systems, including cartridge-type microfilters and filter-coalescers, at different points between refinery and aircraft fuel tank in order to remove dirt (particulates) and water and ensure that contamination levels always meet the required specifications. The main objective of the present study was to apply proton NMR relaxometry to provide insight into the water coalescence process, specifically by probing water environments on fibrous media. On the basis of T-2 (spin-spin) relaxation distributions, it has been confirmed that the water environments depend on the media wettability, with three environments being identified: fiber surface adsorbed water,; interfiber absorbed water, and unassociated (largely bulk) water. The use of such NMR techniques may therefore offer potential for monitoring or improving filter-coalescer performance.