Rainwater harvesting involves collecting and storing rainwater in a controlled manner from sources like rooftops and open spaces. It has several benefits like improving groundwater levels, reducing drought and flood impacts, and providing fresh water. There are three main methods - rooftop harvesting, open space harvesting, and groundwater recharge. Rooftop harvesting collects rainwater from building roofs while open space harvesting creates ponds in parks. Groundwater recharge filters and directs rainwater back into the soil to replenish underground water levels. Watershed management conserves rainwater across different scales from micro to macro levels and aims to efficiently use natural resources.