Sand dams are a simple and cost-effective rainwater-harvesting technique which can provide a lifetime supply of clean water within 30 minutes of people’s homes. They can save up to 11.5 hours each day (otherwise spent on collecting water) in periods of drought. A sand dam is a reinforced stone masonry wall built across a seasonal river. During the rainy season, a seasonal river forms which carries soil (composed of sand and silt) downstream. The heavier sand accumulates behind the dam while the lighter silt is carried downstream. Within one to four rainy seasons, the dam completely fills with sand. However, up to 40% of the volume behind the dam is actually water, held in the pores between the sand particles. Because water is stored within sand, it is protected from evaporation, contamination and disease vectors. A mature sand dam can store up to 40 million litres of water, recharging groundwater and providing a clean, reliable and local source of water all year round for up to 1,000 people. Sand dams have virtually zero operation and maintenance costs and last for over 50 years. They are widely suited to dryland regions of the world. By working with local partners, this project has helped 479,990 people gain improved access to clean water close to their homes by building sand dams and using other simple rainwater harvesting technologies