What is storm water run-off?

Storm water run-off is generated from rain or melting snow that flows across land or impervious surface instead of seeping into the ground. As it flows, run off can pick up and carry substances that pollute water. These substances include chemicals such as pesticides, fertilizers, oil, etc. as well as natural material like sediment, bacteria, leaves and garbage. In developed areas, precipitation falling on impervious surfaces like roofs, driveways and parking lots does not seep into the ground, it runs off. Polluted storm water runoff is the major cause of water pollution.