The SWC is available as a mobile web-based application or as a desktop program-both versions require an internet connection. The SWC is designed for use by anyone interested in reducing runoff from a property, including site developers, landscape architects, urban planners, and homeowners. Help control runoff and promote the natural movement of waterĮPA’s National Stormwater Calculator (SWC) is a software application tool that estimates the annual amount of rainwater and frequency of runoff from a specific site using green infrastructure as low impact development controls.