Arsenic in drinking water is a huge problem in many areas of South Asia and the western US. The elevated level of drinking-water arsenic has seen massive epidemics of arsenic poisoning in recent years. Arsenic can be removed from drinking water by using activated carbon or precipitating it out with iron minerals, such as iron oxides such as magnetite (Fe3O4) nanocrystals. However, such particles cannot be used in large water bodies such as rivers or other environments where water flows, because of their small size and the fact that magnetite rapidly oxidises when exposed to the atmosphere. Researchers in Korea have recently overcome the latter problem by combining iron oxides with carbon and carbon nanotubes, and graphene-based materials such as graphene oxide. The magnetite-RGO composite can be dispersed in water and after adsorbtion of arsenic, it can quickly be removed using a permanent hand-held magnet (with a strength of 20 mT) within a fraction of a minute.