Gutter: WHAT IT IS: It is a narrow channel, or trough, forming the component of a roof system. WHAT IS DOES: It collects and diverts rainwater shed by the roof. In many buildings, the purpose of this diversion is to prevent water from falling off the roof edges. Downspout: WHAT IT IS: They are the vertical pipes used for conveying rain. WHAT IT DOES: The gutters are sloped that point towards the vertical downspouts and drain the collected water.