Rainwater harvesting is one of the simplest and most effective ways to tackle water scarcity. Yet most rooftops still waste this resource, even though systems can cut household fresh-water use by 30–60%, supplying toilets, laundry, and gardens with ease. They also help prevent flooding, and today’s smart systems optimize storage automatically. Germany shows what’s possible, with over a million systems already in place and three-quarters of all new housing now being built with rainwater capture