Self-assembled polymeric nanoscale systems that are robust yet adaptive are of primary importance for fabricating multifunctional stimuli-responsive nanomaterials. Noncovalent interactions in water can be strong, and biological systems exhibit excellent robustness and adaptivity. Synthetic amphiphiles can also result in robust assemblies in water. Can we rationally design water-based noncovalent polymers? Can we program them to perform useful functions that rival covalent materials? We review here advancements related to these questions, focusing on aromatic selfassembly in aqueous media. Regarding functional materials, we present examples from our work on water-based recyclable noncovalent membranes, which can be used for size-selective separations of nanoparticles and biomolecules. These systems introduce the paradigm of noncovalent nanomaterials as a versatile and environmentally friendly alternative to covalent materials. We also address emerging rational design principles for creating 1D, 2D, and 3D functional nanoarrays hierarchically assembled from welldefined molecular units in aqueous media, enabling new synthetic strategies for fabricating complex water-based materials.