The capturing of water contaminants and the remediation of water bodies is an important concern to human health due to severe side effects of contaminants on the body such as cancer. Pharmaceuticals, heavy metals, dyes, and chemical warfare agents (CWAs) are a few of the toxic pollutants that cause serious damage to the environment, humans, and animals. Meanwhile, scientists in the fields of polymer nanotechnology and nanoscience have been investigating tremendous solutions for eliminating water pollution to ensure environmental safety. Among all methods of water purification, adsorption is an important and versatile technique for remediation and has been used to remove toxic elements from water-based materials for many years. Using polymer-based materials as an adsorbent is very common to purify polluted waters. The main factors to evaluate adsorbent performance are adsorption capacity (maximum contaminant uptake by adsorbent), adsorption rate (how fast the adsorbent adsorbs contaminants), contaminant selectivity (adsorption of a specific contaminant among other ones), and adsorbent reusability (ability of adsorbent to remove contaminants in consecutive order), which are compared in this work. These factors are affected by pH, temperature, contact time, and also type, dosage, and morphology of the adsorbent. Natural and synthetic polymers in different types of films, membranes, nanocomposites, porous materials, and hydrogels with functional groups such as hydroxyl, amine, carboxyl, and amide are used as a selective material to adsorb water contaminants. Serious needs to remediate the water base from several contaminants direct the researchers to utilize polymer-based adsorbents with the ability to adsorb multiple contaminants simultaneously in the shortest possible time. This work reviews different water contaminants and their removal mechanisms and detection using nanodevices and polymer-based adsorbents.