Abstract: An exemplary system includes a rainwater cistern and a first heat pump loop configured to transfer thermal energy between water stored in the cistern and an indoor medium. The first heat pump loop may further be configured to selectively transfer thermal energy between the indoor medium and an outdoor medium. Additionally or alternatively, the system may further comprise a second heat pump loop configured to transmit thermal energy between the stored water and the outdoor medium. In certain embodiments, the system may include a spray system operable to spray collected water over the roof of a building.