The process of water treatment reduces or removes biological and chemical pollutants that could endanger the human water supply. A novel class of intelligent materials known as stimuli-responsive polymers is employed in water treatment through a purification process that is triggered and followed by polymer regeneration. When the environment changes, the physicochemical characteristics of stimuli-responsive polymers dynamically change. Depending on the applied stimulus, they can expand or contract, change their optical qualities, and modify their electrical properties. In this context, water treatment can make use of a variety of stimuli-sensitive polymer systems, including hydrogels, membranes, porous nanoparticles, supramolecular polymers, self-assembled nanostructures, and responsive coatings. Researchers are quite concerned about heavy metals and dyes since they are two major drivers of water pollution. These pollutants are ineffectively removed from water by current procedures, which could jeopardize the ecosystem. This chapter focuses on stimuli-responsive polymers, which exploit their responsive properties to absorb dyes, aqueous anions, and heavy metal ions.