Santiago's Turbidity Alert and Raw-Water Reserves
Most of Gran Santiago drinks Andean river water, and Andean storms are the problem: a cloudburst or landslide in the cordillera can push raw turbidity in the Maipo far past what a treatment plant can handle. Aguas Andinas, the private concessionaire that supplies the city and most of the metropolitan area, has cut supply to more than a million customers repeatedly, in February 2013, April 2016 and February 2017. Its answer was storage plus an alert. Six raw-water tanks at Pirque holding 1.5 million cubic metres entered service in December 2019 and were inaugurated by the public works minister in November 2020; with the Cerro Negro and Lo Mena wells they give the city 37 hours of production without touching a river, against 11 hours before. When cordillera weather and river readings turn bad the utility declares a preventive early alert, stops intake and runs the Las Vizcachas and La Florida plants on stored water. Nothing published makes that switch automatic; an operator decides. The buffer has held through repeated alerts since 2021, and it was overrun once: on 24 June 2023, after 280 mm of rain in four days, autonomy fell by half and 1,304,857 customers in 34 comunas lost supply anyway. Maipu and Cerrillos, served by the municipal utility SMAPA, sit outside this system.
📊 Impact
Aguas Andinas puts autonomy at 37 hours, from six Pirque tanks of 1,500,000 cubic metres costing about US$100 million plus the Cerro Negro and Lo Mena wells, against roughly 11 hours before them and about four hours in 2011; those figures are the operator's own, restated by the Ministry of Public Works at the November 2020 inauguration, and no independent audit of them was found. The events they answer are better documented. The Maipo normally runs between 40 and 500 NTU and the Las Vizcachas plant can treat to roughly 20,000 NTU, but February 2013 recorded 380,000 NTU and cut 1,128,044 customers, April 2016 reached 79,000 NTU and cut about 4.2 million residents across 29 comunas, and February 2017 hit 33 comunas. CIPER Chile found that customers had already paid about US$10 million through a 1.06 percent tariff rise for an earlier phase of works meant to prevent exactly this, which lifted autonomy from 3.3 to 13 hours. The regulator has acted: the Superintendencia de Servicios Sanitarios sanctioned the utility about US$1.7 million over the January and February 2013 cuts. Since the tanks opened the record is mixed, with alerts in 2021, 2022, 2023 and July 2026 passing without a cut and the 24 June 2023 storm cutting 1,304,857 customers regardless.
🎓 Lesson
Storage buys hours, not immunity. Reserves turned most turbidity events into a non-event, then the largest storm in decades halved the buffer and the cut happened anyway. Because the switch to reserves follows a declared alert and an operator's decision rather than an automatic threshold, the ceiling on this system is the size of the tank, not the speed of the alarm.
Sources
📎 Cite this project
1001 Smart Cities (2026). “Santiago's Turbidity Alert and Raw-Water Reserves” — Santiago, Chile. The Smart City Atlas. https://1001smartcities.org/projects/santiago-water-turbidity-response/ (last verified 2026-07-26). Data: CC BY 4.0.
The underlying data is free to reuse with attribution — see the open data page.
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