Toronto cools 200 downtown buildings with cold water from deep in Lake Ontario

The system, operated by local energy provider Enwave, began in 2004 with the launch of its Deep Lake Water Cooling (DLWC) network. Drawing water from approximately 83 metres below Lake Ontario’s surface, where temperatures are reliably cold even during the hottest summers, the company established what was then North America’s largest district cooling system utilizing a natural body of water. At the time it began operations, the project provided enough air conditioning for 20 million square feet of office space, according to the Daily Commercial News.

Instead of circulating lake water directly through building air-conditioning systems, Enwave uses a network of underground pipes and heat exchangers. The process starts at the Island Filtration Plant, where water from the lake is pre-treated. This chilled water is then transferred via the John Street Pumping Station, where heat exchangers absorb and transfer the cooling energy from the lake water into a separate closed water loop. This chilled water is distributed through roughly 40 kilometres (25 miles) of pipes running beneath downtown Toronto.

Once the chilled water reaches participating buildings, it absorbs heat from their internal systems. The now-warmed water is piped back into the district cooling network, where it is cooled again before being circulated back into the system. Because the lake water never mixes with the water that enters the buildings, quality and safety are maintained.

Enwave reports a 75 percent reduction in electricity usage when compared with conventional air conditioning systems, alongside an estimated annual elimination of 40,000 tonnes of carbon dioxide emissions in Toronto. This approach has reduced the need for individual buildings to operate their own energy-intensive cooling towers and chiller plants, offering substantial capital and operational savings for major downtown customers such as Brookfield Place, as well as hospitals, data centres, hotels, and educational institutions. As of today, the network serves more than 200 buildings and over 40 million square feet of downtown real estate, supported by four interconnected plants.

Toronto’s Deep Lake Water Cooling system is a leading example of how natural resources can be integrated into urban energy infrastructure. By relying on the enduring cold of Lake Ontario, the city eases the burden on its electrical grid and avoids the spikes in demand typically seen during summer heat waves. Now more than 20 years since its inception, the system continues to expand, signalling the potential for sustainable, centralized energy solutions in other densely populated urban areas facing similar challenges as global temperatures rise.