Paris expands underground chilled‑water cooling network and opens Seine swim spots as heatwave hits record

Paris has built a more than 120‑kilometre underground network that circulates water at 2‑4 °C to cool the basements of roughly 1,000 public and private buildings, including offices, museums, hospitals and schools. The system returns warmed water to specialised plants for re‑chilling and uses the Seine as a heat‑exchange resource, allowing the city to cut electricity use compared with conventional air‑conditioning and to address health risks from extreme temperatures. The public‑private "Fraîcheur de Paris" scheme plans to triple the network’s reach by 2042.

At the same time, the city has opened three designated swimming areas on the Seine for residents and tourists, marking the second consecutive summer the river‑ban has been lifted. The move follows a €1 billion wastewater‑treatment overhaul that restored water quality, enabling safe public bathing after a century‑long prohibition. The swim spots were timed to commemorate 250 years of Franco‑American friendship and provide relief during a record‑high temperature of 104 °F (40 °C).