Researchers in South Africa have developed a nature-based water treatment system that is helping transform heavily polluted river water into a resource suitable for irrigating vegetable gardens, offering what scientists say could become an important model for improving food security as climate change intensifies water shortages.
The project, being carried out by researchers from the University of Cape Town in the Langrug informal settlement near Stellenbosch in the Western Cape, uses a combination of stones, sand and heat-treated wood instead of chemicals to clean contaminated water from the Stiebeuel River. The system currently treats about 36,000 litres of water every day, removing pollutants from water affected by sewage, chemicals and traces of pharmaceutical and medical waste.
Although the treated water is not considered safe for drinking, researchers say it has now reached a quality level suitable for irrigation. Around 3,000 litres of the treated water is retained for use in food-producing gardens at the Water Hub, while most of the remaining water is returned to the river after treatment. According to the researchers, the system can remove nearly 99% of toxins from the water.
The initiative, known as the Water Hub project, was established in 2018 in response to growing water and sanitation challenges in Langrug. The settlement has expanded dramatically over the years, with its population increasing from around 3,000 people in 2006 to more than 26,000. Much of the growth has been linked to seasonal employment opportunities on farms and in the nearby town of Franschhoek.
The rapid and largely unplanned expansion placed significant pressure on existing water and sanitation infrastructure. Residents faced inadequate access to clean water and sewage facilities, while conventional treatment plants struggled to cope with the growing demand. Researchers subsequently converted an abandoned wastewater treatment site into a system of filtration beds.
The treatment process is powered by solar energy, allowing the facility to operate off the electricity grid. Water is pumped from the polluted river into a series of filtration cells, where it moves slowly through different layers over a period of about five days. Large stones initially trap particles and certain chemicals. The water then passes through biochar, a form of heat-treated wood produced by burning wood at about 800C, which helps remove pharmaceutical residues, traces of drugs and ammonia. Smaller stones and sand provide additional filtration before the treated water is released.
Researchers say the approach is not intended to replace large conventional treatment plants that supply major towns and cities or handle industrial-scale volumes of wastewater. Instead, its value lies in providing a relatively affordable and environmentally friendly option for smaller or rural communities facing water shortages and inadequate infrastructure.
The project has also gained importance because of the growing threat posed by climate change to water availability and agriculture. The Western Cape experienced a severe water crisis in 2018 after prolonged drought caused reservoirs to approach critically low levels. Residents were forced to ration water for months, while the agricultural sector suffered major economic losses, including the loss of jobs for thousands of farm workers.
Scientists involved in the project believe such experiences demonstrate the need to rethink how communities manage wastewater and secure supplies for food production. With climate models pointing towards greater variability, including longer droughts alongside intense flooding and wildfires, access to water for agriculture is expected to become an increasingly important challenge.
Kevin Winter, one of the researchers associated with the Water Hub project, said making treated water available for food production could become an important part of climate adaptation strategies. The project demonstrates how wastewater that would otherwise contribute to environmental pollution can instead be treated and reused to support local food production.
The researchers believe the experience in Langrug could have wider applications in communities facing similar combinations of rapid population growth, water pollution, inadequate infrastructure and climate-related water stress. By relying on natural filtration materials and renewable energy, the system provides an alternative approach that could be adapted to local conditions.
As climate change increases pressure on freshwater resources, projects such as the Water Hub highlight the potential of treating wastewater not simply as a problem requiring disposal, but as a resource that can support ecosystems and local agriculture. Scientists say expanding such approaches could help vulnerable communities prepare for a future in which both clean water and reliable food supplies are increasingly threatened.
