Aquifer thermal energy storage (ATES) is a low-temperature geothermal energy source. ATES has been used successfully around the world for the seasonal storage of heat and cold energy for the purpose of heating and cooling buildings. Large-scale ATES systems are not used widely in Canada, however, ATES has been successfully implemented at the domestic scale, particularly in Ontario. The Pacific Agricultural Research Centre in Agassiz, BC, Carleton University in Ottawa, the Sussex Hospital in N.B., and the Scarborough Centre in Ontario are examples of large-scale sites where ATES systems are in operation. Through consulting and research activities, I have been actively involved in the design (well field) of the ATES systems at Agassiz and Carleton.