Detecting the coronavirus in samples from treatment plants could give early warning of outbreaks and new variants. By Heather Richardson

Monday is sample-collection day in Cape Town, South Africa, and Aqeelah Benjamin is halfway through her shift. At the Green Point wastewater-treatment plant, under the Atlantic coast promenade, she fills a 500-millilitre bottle from a tap of untreated water. She wipes the bottle’s exterior, cleans it with a spritz of ethanol and stores it on ice. It’s one of nine samples that Benjamin will collect today, each from a different facility. Later, she’ll drop them off at the South African Medical Research Council (SAMRC) laboratory, where they will be tested for the presence of SARS‑CoV-2, the virus that causes COVID‑19. But that’s just a fraction of the samples’ potential — waste water contains a wealth of information about public health, and scientists are only just starting to tap into its potential.