Quality water is becoming scarce, and decontamination methods are often costly. However, there is the possibility of using waste from agro-industrial activities to develop materials with high potential for application and water purification. Among the components present in these residues, cellulose and, more specifically, cellulose nanofibers have been highlighted. Under these conditions, cellulose exhibits a high surface area, good chemical reactivity, high mechanical strength, and allows the production of a high number of by-products obtained by different chemical reactions. That, at the end of it, provides applications in water decontamination. From this perspective, this chapter provides specific information about cellulose nanofibers, exploring aspects of the different treatments that allow them to be obtained. Of the main chemical reactions that have been used to produce materials with decontamination potential for the metal cation lead(II) and dyes. For this, works from the literature were used aiming exclusively to understand some aspects that help to highlight which variables help to better enhance the process of removal of these mentioned contaminants.