Filters that are structured on the nanoscale offer the promise of better water purification systems. They are cheap to manufacture, long-lasting and can be cleaned. Other similar technologies could absorb or neutralise toxic materials, such as arsenic, that poison the water in many countries including India and Bangladesh. Tiny wastewater filters, for example, could sift emissions from industrial plants, eliminating even the smallest residues before they are released into the environment. Similar filters could clean up emissions from industrial combustion plants. And nanoparticles could be used to clean up oil spills, separating the oil from sand, removing it from rocks and from the feathers of birds caught in a spill.