The Gutter Shutter system has been designed and tested to handle even the heaviest rainfalls. The hood of the Gutter Shutter system has flow reducers that slow the water coming off your roof. However, it’s the principle of surface tension that keeps the water flowing into the gutter. Surface tension isn’t affected by the amount or speed of the water flowing. Even in the heaviest rainfalls, Gutter Shutter works great.