Water pollution is a serious environmental and public concern all over the world. Many toxic metals (e.g., lead and cadmium) even at trace levels are believed to have adverse effects on human health. Thus, it is important to develop efficient technologies for enhanced removal of toxic metal ions from contaminated waters. Various technologies have been developed for the decontamination of water. Nanocellulose has attracted a great deal of interest as a source of nanometer-sized materials because of their biodegradability, easy availability, and the related characteristics, such as a very large surface-to-volume ratio and outstanding mechanical properties. This article assembles the current applications of nanocellulose in the environment, namely as an adsorbent for heavy metals, water purification, antimicrobial and catalytic activities, and a reinforcement for biodegradable materials. Water pollutant remediation by catalytic decomposition of organic pollutants is a growing application of nanocellulose-based nanocomposites.