For more information on storm water pollution, click images below... What is Stormwater Runoff? Water that does not soak into the ground or evaporate is called stormwater runoff. Stormwater runoff flows over the ground surface and then into storm drains and ditches that empty directly into our local waterways. This is especially true in cities, villages, and other developed areas because water can't soak through the pavement, rooftops, and concrete. This means that there is more stormwater runoff generated in cities and villages than in forests and fields.