UN taps river water to cool headquarters as sustainable alternative to air conditioning

Deep beneath the United Nations headquarters in New York, a decades-old but efficient cooling system quietly harnesses the East River’s water to help regulate the building’s temperature—offering a low-energy alternative to traditional air conditioning.

This water-based system, which has been part of the UN complex since it opened in the 1950s, uses as much as 26,000 liters (7,000 gallons) of river water per minute, circulated through fiberglass pipes and a refrigerant system to produce cool air. Updated during a major renovation from 2008 to 2014, the system now plays a vital role in maintaining a consistent indoor temperature of around 24°C (75°F), while consuming significantly less energy than standard AC units.

In the sweltering summer months, when New York’s air can reach 38°C (100°F), the East River—technically a saltwater estuary—remains much cooler. This natural temperature differential makes the system more efficient. Two separate water loops prevent any contamination of the water before it’s returned to the river at a warmer temperature.

UN engineers Michael Martini and David Lindsay, who oversee the operation, point out that despite the headquarters’ modern appearance, this cooling system is largely invisible—and yet crucial to the complex’s sustainability.

The UN’s use of water-based cooling doesn’t stop in New York. In Geneva, the Palais des Nations uses water from Lake Geneva, while in Copenhagen, UN City relies on seawater for nearly electricity-free cooling.

With over two billion air conditioners in use globally—and demand expected to grow amid rising temperatures—such alternatives are gaining attention. According to the International Energy Agency, energy use for cooling has tripled since 1990, sparking a call for more efficient technologies.

District cooling systems like the UN’s—powered by lakes, rivers, or even seawater—are not widely implemented, despite their benefits. These systems reduce the need for toxic refrigerants, minimize emissions of hot air into cities, and avoid many inefficiencies associated with standalone AC units.

Lily Riahi, coordinator of the UN-backed Cool Coalition, says wider adoption is hindered by logistical hurdles. “These systems often require extensive coordination between cities, utilities, and other stakeholders,” she explained.

Rob Thornton, president of the International District Energy Association, added that success depends on strong leadership to “aggregate the market”—a model seen in cities like Paris, where the Seine River supports Europe’s largest water-based cooling network.

Still, environmental concerns remain. Returning warm water to rivers can harm aquatic ecosystems. But Riahi notes that the risk is relatively low and manageable, especially when compared to thermal discharges from nuclear plants. She suggests regulating the temperature of discharged water to reduce environmental impacts.

As cities search for sustainable ways to stay cool in a warming world, systems like the UN’s offer a proven, though underutilized, model.