Waste-derived nanoadsorbents are emerging as a strategic class of circular economy materials that transform agricultural residues, food-processing by-products, municipal biowaste, and mineral-industrial residues into high-surface-area adsorbents for water purification. This review compiles and summarizes the recent research related to the design, characterization, adsorption capacity, regeneration and environmental translation of sustainable nanoadsorbents that are derived from waste. The manuscript emphasizes the carbonaceous nanomaterials, biochar magnetic hybrids, egg-shell and zeolite-based composites, chitosan, carbon-dot membranes, cellulose nanomaterial architectures, green-synthesized metals, metal-oxide nanostructures, and geopolymers. Specific contaminants of concern (COCs) such as nickel, cadmium, chromium, lead, dyes, antibiotics, per- and polyfluoroalkyl substances (PFAS) related compounds, and microplastics receive special attention. The review demonstrates that, when precursor chemistry, activation process, nanoscale morphology, surface functionality and regeneration method are optimized together, the uptake of pollutants by Waste-to-Nano Adsorbents (WNAs) can be enhanced to a high level. The full-scale implementation is limited due to the heterogeneity of the feedstock, the lack of complete life cycle assessment, inconsistent adsorption testing, risk of particles releasing from the material and limited field validation. The main message is that Waste-to-Nano Adsorbents (WtNA) should be evolved to be a platform rather than a series of stand-alone laboratory demonstrations, encompassing green synthesis, mechanistic characterization, circular regeneration and techno-economic assessment.