Rainwater harvesting for drinking is an effective method for the shortage of water problems. Rainwater harvesting becomes the primary water source for potable uses, including drinking, bathing, and cooking. Furthermore, some areas have groundwater with contaminants, and water can’t be used for drinking due to heavy metals mixing. So, rainwater harvesting provides a safe drinking purpose. By treating the collected water from rain, it can be used for safe drinking purposes. The rainwater harvesting system’s main process for drinking purposes is rainwater collection, storage, and treatment. The treatment of collected rainwater can be done by developing a filtration system. Tertiary treatment is an essential process after the filtration of rainwater for improving water quality. Implementing a safe drinking system from the rainwater harvesting method help to achieve a sustainable water management system in Sri Lanka.