The key components of a rainwater harvesting system integrated with HVAC systems include a rooftop or surface collection system, gutters and downspouts, a pre-treatment system (e.g., screens, filters), a storage tank, a pumping system, and a treatment system (e.g., disinfection, sedimentation). Additionally, the system must be designed to interface with the HVAC system, including cooling towers, evaporative coolers, and ground source heat pumps.