Rainwater is often seen as waste to be disposed of; it slides off the concrete and asphalt in our cities and is flushed into sewers and storm drains. But rainwater is a vital resource that can be captured and used. Metropolder, recently acquired by Wavin, builds green roofs that capture and store rainwater, from irrigating the greenery on the roof itself to cooling the building down in summer. Here’s how rainwater harvesting can save our cities from the water crisis.