Clean drinking water is vital to human existence, and forests provide the majority of potable water to the public. Urbanization of water-providing forests impacts water quality, as traditional urban development practices eliminate tree canopy cover, remove existing ground cover and pervious soils, and compact the remaining soil to better accommodate impervious surfaces. Green Stormwater Infrastructure (GSI) practices in municipalities are becoming viable strategies for managing stormwater runoff for less money compared to conventional stormwater conveyance practices. However, little is known about the benefits of urban forest systems as a GSI practice for stormwater volume control and water quality. Current research provides valuable information that stormwater professionals can use to mitigate urban stormwater runoff. The Forest Service worked with civil engineers to compile research regarding urban trees and stormwater benefits. These manuscripts reviewed the most current research regarding the volume of rainfall retained by tree canopy; the impacts of foliar detention on stormwater runoff lag time, peak flow, and velocity; water volume removed from the soil through transpiration; and, nutrient uptake by trees. These functions assist in “pre-treating” stormwater, helping to remove pollutants before it enters our drinking water supply. This research quantified the stormwater runoff reduction function of trees and discussed a method for estimating tree function and equating to best management practices design capacity. The information gives stormwater and other natural resource professionals a way to quickly estimate tree impacts on stormwater and equate to the function of engineered systems. Ultimately, this gives them a basis for including urban forest systems in their stormwater management plans and design projects.