The area around Lima, Peru, is facing a water shortage and the country is turning to a dike system created by a pre-Incan civilization. Called amunas, these dikes were created around 600 B.C., and they divert excess water from streams that during the rainy season would otherwise flow uncontrolled down the mountains and eventually be lost in the Pacific Ocean. Instead, thanks to the amunas, the water will infiltrate the soil, replenish the water table and ensure its gradual release throughout the year in natural springs. The ancient technology also improves water purity and helps prevent erosion and landslides. The amunas are being excavated and returned to use; a complementary project is focused on restoring the puna, the high-altitude tundra ecosystem that, when healthy, holds water like a sponge. These green measures can cost 100 times less per cubic foot of water investing in gray infrastructure such as dams and reservoirs.