What is stormwater runoff, and why does it matter?

What is stormwater runoff, and why does it matter?

How pollution gets into stormwater

Right from the start of our expedition, stormwater runoff has held center stage when it comes to water quality issues. It's a constant refrain: Tell us about the water quality issues that this watershed faces? Answer: Stormwater runoff.

More than three quarters of North Americans live in urban areas, and by 2030, 60 percent of the world's population is expected to live in them. Not only do these concrete jungles alter our watersheds and hydrological cycles, but they also shunt the runoff from impervious pavement and rooftops, into the water body at hand, whether it's a lake, creek, river or coastline.

"People think storm water is pristine," says Lou Di Gironimo, general manager for Toronto Water. "Well, it is when it comes out of the clouds but not when it hits an urban surface." Despite the fact that Toronto's stormwater does not meet the criteria for discharging it untreated, the bulk of it is collected in storm drains and funneled straight into the city's creeks, rivers and lakes, like in so many urban centers worldwide.

According to the Environmental Protection Agency, some 80,000 miles of streams and rivers are impaired by urbanization in the U.S. And the amount of impervious surface superimposed on the country's watersheds ranges between 12.5 percent and 30 percent—high enough to degrade aquatic habitats.