You've probably heard of a green roof, which sits on top of a building and is covered with vegetation. But what about a blue roof? You might have guessed that it has something to do with water. Indeed, a blue roof collects stormwater through a pond system, temporarily stores it and gradually releases it afterward — offering a way to conserve water and prevent water damage. During a storm, rainwater can overwhelm urban sewer systems and send contaminated, untreated water into lakes and rivers. A blue roof could help solve this problem.