Concept:Rainwater harvesting is the method of collecting and storing rainwater for later use. It helps conserve water and recharge groundwater.Explanation:Rainwater is the main source of water that fills rivers, lakes, and groundwater. When it rains, water flows away and is wasted. In rainwater harvesting, this excess water is collected in tanks or directed underground through pipes. This recharge groundwater and increases its level. The stored water can be used for drinking, irrigation, or other purposes. It reduces water scarcity and pollution.Answer:Rain water harvesting (Option D)