In July 2026, irrigators on the Mapocho asked a civil court to void the 2021 agreement behind Aguas Andinas' plan to send up to 3 m³/s of treated wastewater from its Mapocho-Trebal biofactory to the Maipo River. In exchange, Maipo irrigators would give the company raw water to treat for Santiago.
Why the swap matters
Aguas Andinas owns only about 28% of the water rights of the Maipo, its main surface source, according to its May 2026 corporate presentation. In a drought it cannot simply take more river water. Its August 2021 agreement with irrigator organizations of the First Section of the Maipo lets irrigators transfer water to the city during droughts, with priority for human consumption.
The company says the exchange, known as Retorno Maipo, would raise customer bills by about 2%, against 25% to 30% for desalination.
What the plaintiffs argue
The Junta de Vigilancia of the Third Section of the Mapocho and the Mallarauco canal association argue that a concession holder cannot dispose of treated wastewater, and that redistribution should run through the Water Code and public basin planning. They estimate losses of about US$45.3 million a year on 2,696 hectares in the Mallarauco valley.
The wider picture
The dispute lands as Chile's first Climate Change Adaptation Plan for Water Resources, with 10 measures and 35 actions, was published in the Diario Oficial in September 2026. The El Yeso reservoir, the main drought buffer, fell from 89.5% of capacity at the end of December 2025 to 64.9% at the end of June 2026.
How the lawsuit fits with Aguas Andinas' wells, storage and tariff-funded climate works, what its 7.4% works tariff pays for, and which tests will decide its move from service provider to system operator are examined in the full report. The full report, Water Utility of the Future: Aguas Andinas, is available for USD 499. For a free overview, read the Aguas Andinas Utility Snapshot.