South Korea to expand water-source heat energy to groundwater, wastewater and industrial water

South Korea is pushing to tap previously unused water resources — including groundwater seepage, sewage, wastewater and industrial water — as sources of water-source heat energy, in a bid to accelerate the country's drive toward carbon neutrality.

The Ministry of Climate, Environment and Energy said Tuesday that an amendment to the enforcement decree of the Act on the Promotion of the Development, Use and Diffusion of Renewable Energy was approved at a Cabinet meeting and is set to take effect Nov. 17.

Thermal energy accounts for 48 percent of domestic energy consumption and 29 percent of greenhouse gas emissions, making it one of the country's highest-emitting sectors. Diversifying water heat sources is widely regarded as a key lever for driving low-carbon transitions in buildings and industry.

Water-source heat energy exploits the fact that water temperatures are lower than ambient air in summer and higher in winter, making it suitable for building heating and cooling. The technology can cut energy use by more than 30 percent compared with conventional heating and cooling systems.

However, existing projects have largely been confined to areas near rivers, dams or major water supply pipelines, limiting their expansion into urban centers and inland industrial complexes where heat demand is concentrated.

To remove those constraints and promote broader use of water-source heat energy, the government is amending the enforcement decree to create a legal basis for designating additional water resources with stable temperature and volume through official notice. It is also issuing a new notice that adds seven previously untapped water heat sources as renewable energy: groundwater seepage, sewage, treated sewage effluent, wastewater, treated wastewater effluent, reprocessed sewage and wastewater treatment water, and industrial water.

Underground development projects — subways, tunnels and large buildings — generate an average of about 581,000 tons of groundwater seepage per day nationwide, which can be used to supply heating and cooling energy for the buildings themselves.

Heat can also be recovered from treated sewage effluent and industrial wastewater, which maintain temperatures of 12 to 15 degrees Celsius in winter and 20 to 25 degrees in summer, and supplied as district heating or process hot water. This would help reduce urban heat island effects and cut fossil fuel use.

If all discharge water from wastewater treatment plants nationwide handling 500 cubic meters per day or more — totaling about 20.09 million tons per day — were utilized, the potential energy yield is estimated at 3 million Gcal per month, enough to heat approximately 3 million households.

In the case of industrial water, only heat is extracted before the water is returned 100 percent to existing industrial processes, allowing a stable and continuous supply of industrial water with no loss or consumption of water resources.

Beyond the seven newly designated sources, the government plans to continuously identify and designate additional potential water heat sources, and to pursue pilot projects supporting the expansion of sewage heat systems.

Song Ho-seok, director general for water management policy at the Ministry of Climate, Environment and Energy, said water-source heat energy had already proven its effectiveness through pilot projects at venues including the Korea International Trade Association building and Lotte World Tower. "Building on this regulatory overhaul, we expect water-source heat energy to spread widely to demand sites near urban buildings and industrial complexes throughout the country," Song said. "We will continuously uncover water heat sources hidden across various sites to provide solid support for carbon neutrality in the thermal energy sector."