Abstract: Embodiments of the invention relate to systems and methods for the harvesting and treatment of rainwater for secondary use within buildings. Rainwater is harvested utilizing a rainwater capturing device and stored in a cistern prior to treatment until a demand for secondary use is made. The rainwater may be combined with reclaimed water from a water treatment plant. Once a demand for secondary use is made, the water is subjected to treatment as it travels to the point of use. Treatment includes neutralizing the pH of the rainwater, filtering the rainwater to remove particulate matter, irradiating the rainwater with ultraviolet light, and introducing a chlorine solution into the rainwater.