Cape Town researchers turn polluted river water into irrigation using natural filters

A team led by Kevin Winter at the University of Cape Town repurposed an abandoned wastewater site into a natural filtration system that treats roughly 36,000 litres of Stiebeuel River water each day. The multi-stage process uses large stones, bio-char made from wood heated to about 800 °C, and finer sand to strip out chemicals, drugs, ammonia and other contaminants, achieving about 99 % toxin removal. Powered entirely by solar panels, the off-grid hub supplies around 3,000 litres of clean water for irrigating vegetable gardens in Langrug, a settlement near Stellenbosch that has swelled from 3,000 to over 26,000 residents.

While the water is not deemed safe for drinking, the system reduces bacterial levels to irrigation-acceptable standards and releases the bulk of treated water back into the river, supporting local ecosystems. The initiative offers a low-cost, climate-resilient model for vulnerable communities facing water scarcity and food-security challenges.