The treatment of contaminated water prior to its introduction into surface water is one of the most pressing global challenges of the future. Existing processes for treating water and wastewater can be optimized by suitable nanotechnology applications, which can result in a more targeted removal of contaminants, better energy efficiency and lower costs. Experts predict that the water sector could also benefit most from innovative nanotechnology applications in the medium to long term. In addition to the benefits of using nanomaterials for water treatment, it should also be borne in mind that nanomaterials can have unintended impacts on the environment and human health. When using nanomaterials it is important to note that the novel properties of nanomaterials may possibly also have harmful effects on the environment and humans.