What happens to water in urban areas when it flows down storm drains?

In urban areas, when water flows down storm drains, it typically enters a system of underground pipes designed to manage stormwater runoff. This runoff can carry pollutants such as oils, debris, and chemicals, leading to contamination of local waterways. Unlike wastewater, stormwater is often not treated before being discharged into rivers, lakes, or oceans, which can negatively impact aquatic ecosystems. Additionally, this system can lead to increased flooding if not properly managed, as urban surfaces prevent water from soaking into the ground.