The first global assessment of the role of ecosystems in providing sanitation, conducted by scientists from the UK and India, showed that nature provides at least 18% of sanitation in 48 cities around the world. A study published in the journal One Earth says more than 41.7 million tons of human waste is recycled each year without dedicated infrastructure. Nature purifies wastewater before it enters groundwater.

Wastewater treatment infrastructure that converts human feces into harmless products is an essential tool for global human health. However, in 2017, more than 25% of the world’s population did not have access to basic sanitation facilities, and another 14% used toilets where household waste was dumped on site. While some of this waste is hazardous to local populations, previous research has shown that natural wetlands and mangroves, for example, cleanse them effectively.

The Navikubo Marshes in Uganda treat the untreated wastewater of more than 100,000 households, protecting Murchison Bay and Lake Victoria from harmful pollutants. In the coastal wetlands of the US Gulf of Mexico, nitrogen is removed from the Mississippi River.

To better understand how natural ecosystems recycle waste, scientists from the Universities of Bangor, Cranfield, Durham, Gloucestershire, Hyderabad (India) and the Freshwater Research Center (South Asia) have quantified sanitation ecosystem services in 48 cities, home to about 82 million people. An estimated 2.2 million cubic meters of human waste per year are recycled naturally in these areas. Extrapolating the data, the scientists concluded that nature disinfects about 41.7 million tons of human waste per year before they enter the groundwater.

The findings of the scientists shed light on the important but often unrecognized contribution that nature makes to the daily life of many people. The authors hope that it will inspire the public and policymakers to more actively protect important ecosystems such as wetlands.